THE SEVENTEENTH CENTURY

The explanation for this tension may well lie in the fact that both
mathematicians treated old problems by means of a new symbolic algebra,
without themselves being clear on the extent to which the new means had
changed not only the techniques of solution but also the very manner of
posing problems. With the new algebra, the ars analytica,
mathematicians
thought at first that they had regained the mathematics of the Golden
Age
of antiquity.^{5} Within a short time,
however,
the highest achievements of Greek mathematics had been exceeded, and it
gradually became clear that something brand new was at hand, something
of which the scope was almost limitless.^{6}
In the meantime, mathematicians were subject to the tension mentioned
above.

In the light of the brilliant mathematical achievements of the later seventeenth century , in particular the infinitesimal calculus, there is a risk of overlooking the most important and basic achievement of mathematics at the time, to wit, the transition from the geometric mode of thought to the algebraic. In what follows, we shall investigate this transition somewhat more closely, and we shall do so in two ways. First, we shall analyse the algebraic mode of thought conceptually and offer some examples to document its presence in the early seventeenth century .Then we shall show how the transition to this mode of thought cannot be explained solely by the internal developmental tendencies or needs of mathematics at the time; rather, to understand the transition correctly and to judge its historical importance, the historian must include in his consideration developments in other intellectual areas.

First, then, what should be understood as the "algebraic mode of
thought"?
It has three main characteristics: first, this mode of thought is
characterized
by the use of an operative symbolism, that is, a symbolism that not
only
abbreviates words but represents the workings of the combinatory
operations,
or, in other words, a symbolism with which one operates.^{7}
Second, precisely because of the central role of combinatory
operations,
the algebraic mode of thought deals with mathematical relations rather
than objects. Even when certain relations become themselves objects,
say
the set of group morphisms, one seeks the relations that link these new
objects.^{8} The subject of modern algebra is
the structures defined
by relations, and thereby one may note as a corollary that the
algebraic
mode of thought rests more on a logic of relations than on a logic of
predicates.
Third, the algebraic mode of thought is free of ontological commitment.
Existence depends on consistent definition within a given axiom system,
and mutually compatible mathematical structures live in peaceful
co-existence
within mathematics as a whole. In particular, this mode of thought is
free
of the intuitive ontology of the physical world.^{9}
Concepts like "space", "dimension", and even "number" are understood in
a purely mathematical sense, without reference to their physical
interpretation.
In this respect, the algebraic mode of thought can be characterized as
an abstract mode of thought, in contrast to an intuitive one.

The characteristics of Greek mathematics are almost diametrically
opposed
to those just cited. Greek mathematics almost completely lacked any
symbolism,
much less an operative symbolism. Even in the works of Diophantus one
finds
only a series of abbreviations for the purpose of saving words.^{10}
Paul Tannery once noted that the Greek mathematicians lacked less the
methods
than the suitable formulas for describing the methods.^{11}
He was probably right regarding the lack of a symbolism. But many
methods
depend on the symbolism with which they are expressed, as the
seventeenth
century shows.^{12}

The chief task of Greek mathematics was to discover the inherent
properties
of various geometric figures or of numbers as definite collections of
units.
Only in the analytic reduction procedures by which an unsolved problem
is reduced to a solved one^{13} do we find
any
trace of a relational mathematics, or perhaps also in the first steps
toward
projective geometry in Pappus. That relations stood wholly in the back
of the Greek mind is clear enough from the fact that Aristotle's
Organon
contains no logic of relations.^{14}
Finally,
Greek mathematics was intuitional and strongly dependent on physical
ontology.^{15}
We need only point to the impossibility of multiplying more than three
lines together (the product of two lines was conceived as a plane area,
the product of three lines as a solid, and there were only three
spatial
dimensions), or to the classification of curves according to the
possibility
of their construction by means of straight-edge and compasses (Descartes^{16}
was the first to note explicitly that straight-edge and compasses were,
after all, also mechanical means of construction). Also, the concept of
number as the thing counted, that is, as a collection of counted units,
derived from this basically physical ontology of Greek mathematics.

If, then, the efflorescence of European mathematics in the sixteenth
and seventeenth centuries is largely due to the reintroduction of the
classical
texts, we must nevertheless note that this heritage included a
mathematical
mode of thought diametrically opposed to the algebraic. What became of
this heritage? We find in the seventeenth century an algebra of
quantities
that has a true operative symbolism. We find a theory of equations
which
is based on the conception of an equation as a relation among
quantities
and which serves the purpose of clarifying relations between equations
and their solutions or between the solutions of one equation and those
of others. That is, the structure of algebraic equations is being
examined
and with it such questions as those of solvability are being handled
mathematically
for the first time. We find a loosening, albeit incomplete, of
mathematics
from physical ontology. Clearly visible are a new concept of number and
the overcoming of the dimensional limits of Greek intuition. In** **short,
we find the first foundations of the algebraic mode of thought. Some
examples
may make this clearer.

In** **1591 in his *Introduction to the Analytic Art*, the
mathematician
François Viète introduced a then brand new algebraic
symbolism.
In** **order that the setting up of equations:

...be helped by some art, it is necessary that the given magnitudes be distinguished from the uncertain ones being sought by a constant, perpetual, and highly conspicuous convention, such as by designating the magnitudes being sought by the letter A or some other vowel, E, I, O, U, Y; and the given magnitudes by the letters B, G, D, or other consonants.It^{17}

Viète, however, understood something else by "unknown". True,
following Diophantus he calls it a species, and he calls algebra
logistice
speciosa; but he also says that this "logistic of species" shall be
carried
out using the "species or forms of things".^{20}
The form of the things denoted by alphabetical letters is purely and
simply
quantity: not just numbers or line segments, but everything for which
it
makes sense to say that it is added, subtracted, multiplied, and
divided
(think here of van Roomen's forty-fifth-degree equation that expresses
the problem of dividing an angle into forty-five equal parts).
Viète
is raising algebra from a refined auxiliary technique for solving
arithmetical
problems to the language of mathematics itself.

Thereby, Viète is already pointing past the magnitudes
themselves
to the computational operations and to the ever more complicated
expressions
that can be formed by means of these computational operations. He is
less
concerned with the interpretation of the expressions than with their
structure.
More precisely, he is interested in the structure of the equation that
results from setting two algebraic expressions equal to one another.
For
example, what is the relation between the roots of a given form of
equation-because
of the symbolic differentiation between unknowns and parameters, he can
now study forms of equations instead of individual equations-and the
parameters
of that form of equation? With Viète's algebra, an essentially
new
task of the mathematician comes to the fore: the investigation of the *constitutio
aequationum*, the structure of equations. Thereby, Viète
becomes
the founder of the theory of equations, one of the greatest
achievements
of the seventeenth century, if not the greatest of all.

The themes of Viète's algebra just mentioned find even
clearer
expression in the work of Descartes. Although Descartes insisted
several
times that he had read Viète's *Introduction* only after
the
publication of his own *Geometry,*^{21}hemay
still be viewed as having developed Viète's new ideas farther.
With
regard to symbolism, he differed at first from Vi6te only in that,
instead
of capital letters, he employed the small letters x, y, x for the
unknowns
and a, *b, c *for the parameters (as Fermat often noted, an
arbitrary
convention). But Descartes then went a step farther. He replaced the
last
vestiges of a verbal algebra with a particularly revealing symbolism.
Instead
of writing *2 A cubus, *he wrote 2x^{3}, for which he
gave
the following justification:^{22}*x*
and
*x*^{3} are quantities linked to one another and
ultimately
to a unit by means of certain relations, that is l:*x* = *x*:*x*^{2}
= *x*^{2}*:x*^{3}. Three relations lead from
1 to *x*^{3}, and the number of these relations is given
by
the upper index number. It is here characteristic for a new mode of
thought
that Descartes does not say something like, *x*^{3}
represents
a cube constructed on side *x*, but that he considers this
quantity
simply as a quantity and connects it with a unit according to its
structure.
He goes even farther.

The very first problem in the *Geometry, *published
in 1637, is that of justifying the application of algebra to geometry.
It is treated in the first three pages of the work^{23}
and shows clearly the new mode of thought under discussion here.
Descartes
wants to construct an algebra of line segments and must therefore show
that the six basic operations of algebra (he counts raising to a power
and taking a root, as well as addition, subtraction, multiplication and
division), which in the realm of numerical algebra correspond to the
arithmetical
operations, have a geometrical interpretation. One can, of course, add
any number of line segments, and a smaller segment can always be
subtracted
from a greater. But how does one multiply two line segments together?
Initially,
there is the classical procedure, by which one constructs a rectangle;
a process, by the way, that Viète and (until about 1630)
Descartes
himself used. But a rectangle is not a line segment, and one seeks an
algebra
of line segments. Descartes' answer to this old problem of the
dimensionality
of the computational operations is dazzlingly simple; it follows from
the
concept of powers mentioned above. Assume a unit line segment, to which
all other line segments are referred; if it is not given explicitly by
the problem at hand, it may be chosen arbitrarily.^{24}

To multiply two line segments a and b, one
then needs only construct
a triangle, of which one side is a and the other side is the unit
segment.
In a similar triangle, of which the side corresponding to 1 is b, the
other side, corresponding to a, will be ab. By means
of the
proportion 1:a = b:ab, one sees immediately that ab contains
two relations to the unit length. Put anachronistically - how
anachronistically
remains to be seen - Descartes shows that the line segments (with
multiplicative
unit) form an algebraic field. One is tempted to say that mathematics
is
already on the way toward the investigation of algebraic structures. |

At the same time, the intuitive aspects of algebra diminish.
According
to Descartes (*Geometry, *Book III), every equation *x*^{n}
+ *a*_{1}*x*^{n-1} + . . . + *a*_{n}
= 0 is a complex relation that consists of the simpler relations *x-a*
= 0*, x-b *= 0, ... ,* x-s *= 0*. *Each quantity *a,
b,
c,...s* is a root of the original equation, that is, each may be
substituted
for *x *without disturbing the equality. From experience,
however,
Descartes knows that quite often not all roots of a given equation can
be found numerically or geometrically. For example, if one tries to
factor
the equation *x*^{3} - 1 = 0 into the form (*x - a*)
(*x - b*) (*x - c*)* = *0*, *one finds *a*
= 1,
of course, but no values at first for *b *and c. Nevertheless
such
values must exist or at least be imagined in order for the structural
analysis
of the equation to retain its generality. Hence, Descartes summons his
"imaginary" roots into existence.^{26} He
does
not say much more about these roots, but it suffices for our purposes
that
they exist at all. For, for the first time there appear new, purely
abstract,
non-intuitive objects in mathematics, which arise out of structural
considerations.^{27}
Descartes also frees the concept of number from its classical intuitive
foundations.^{28} From his analysis of the
structure
of algebraic equations it follows that algebra is generally applicable
to numerical problems only if the concept of "number" includes, in
addition
to the integers, fractions and irrationals as well.

There are other examples. From Viète's theory of equations,
for
example, Fermat derives the theorem that, if *P*(*a*) is an
extreme
value of the algebraic polynomial *P*(*x*), then *P*(*x*)
must be of the form (*x - a*)^{2}*R*(*x*); from
this result he develops a method for determining extreme values.^{29}
Later, he derives from Descartes' theory of equations the criterion for
the nature of the extreme, that is, whether a maximum or a minimum.^{30}
His technique of reduction, by which one may determine if a curve
defined
by an equation can be integrated algebraically, is also based on the
theory
of equations as a model.^{31} Not only the
brilliant
techniques of solution, but the very way problems are stated, show that
the main characteristics of the algebraic mode of thought (and thereby
the transition from the classical geometric mode) were already present
in the first half of the seventeenth century. The success and spread of
Fermat's and Descartes' methods made these characteristics the
developmental
themes of mathematics itself at the time.

Now the historically more interesting and more difficult question arises as to why this transition took place at all, and why precisely at the time it did? Of course, the question makes sense only on the presupposition that the development was not in some way predetermined, that it did not, so to speak, lay inherent in the nature of mathematics itself. Then it would merely be a question of the timing of its appearance. But mathematics is not discovered; it is invented, it is created. Symbolic algebra and the mode of thought belonging to it are creations of the seventeenth century and therefore require an historical explanation that goes beyond the timing of their appearance, especially since they differ essentially from the mathematics created by the Greeks. In addition, it seems clear that the complete explanation cannot be found within mathematics alone. The transition to the algebraic mode of thought was not a purely internal development. Why not?

The answer lies in the name that algebra bore in the seventeenth
century:
the ars analytica, the
"analytic art". For Aristotle and for the Greek
mathematicians whose works contributed so essentially to the
efflorescence
of mathematics in the sixteenth century, mathematics was not an art,
not
a *technê*, but a science, an *epistêmê*.^{32}
That algebra and, with it (at least since Viète), mathematics
itself comes
to be seen and designated as an art cannot be explained from within
mathematics.
Second, although analysis was already held by the Greeks to be
constituent
part of mathematics, in antiquity it represented only a heuristic means.^{33}
Only what had been proved by strict synthetic deduction by means of
Aristotelian
logic counted as *epistêmê, *as science. It is clear
why.
Analysis assumes that the theorem to be proved is true or that the
construction
to be carried out has been completed and then pursues the consequences
of that assumption back to an already proved theorem or an already
known
construction. For rigor's sake, however, one must then check to be sure
that all the consequences hold in reverse, and that is the purpose of
synthetic
proof. What one finds in the seventeenth century -- and in ever-growing
measure -- is
analysis in the form of algebra, but without synthesis.^{34}
Hand-in-hand with assurances that an algebraic derivation can always be
reversed to yield a strict synthetic proof,^{35}
the opinion is also expressed that algebra has its own form of rigour.
Hence, one finds in the seventeenth century a new style of mathematics
which has as a characteristic a certain relaxation of the traditional
demand
for rigor. (How else could an infinitesimal calculus resting on such
shaky
grounds have enjoyed such a rapid spread despite the objections of a
Berkeley?)
Since the Greek texts were still being read, this new style bears
witness
to a new conception of mathematics, a conception that had to be
conditioned
by outside forces.

Two general intellectual tendencies of the sixteenth and seventeenth
centuries could have contributed essentially to such a conception of
mathematics:
the pedagogy of Peter Ramus and the search for a *cbaracteristica
universalis,
*a
universal symbolism. The two tendencies have different roots in
antiquity
and in the Middle Ages. The ideas of Ramus are rooted in the rhetorical
tradition of Cicero, which breathed new life into Renaissance humanism,
and in the scholastic liberal arts curriculum.^{36}
A universal symbolism was the goal of the philosophy of Ramon Lull in
the
thirteenth century and continued from that time as part of a
quasi-magical
tradition that demonstrably influenced Francis Bacon.^{37}
The two tendencies were united by Ramus, in whose thought the universal
symbolism lost its connection with magic in favor of a new role as a
symbolic
"art of memory" or means of intuition. Beyond Ramus, indeed probably
through
his influence, traces of these tendencies can be found in the works of
Descartes and later Leibniz. Descartes and Leibniz were mathematicians;
they not only did mathematics, they shaped it.

But let us go back to Ramus, the leading pedagogue of the sixteenth
century. How could he have influenced mathematics? Let us look at the
overall
situation of mathematics before his appearance. At the universities,
the
first six books of Euclid's *Elements
*were being read as preparation
for Ptolemaic astronomy. There the classical tradition of Greek
mathematics
was fostered. Algebra as the "art of the coss" was pursued elsewhere
(with
few exceptions, outside of the universities), for it counted as art,
not
as science.^{38} Beyond that, algebra was
taken
to be a sort of arithmetical solution technique, not for scientific
arithmetic
(that is, number theory), but for "logistic", or computational
arithmetic.
That is, algebra was the concern of the merchant, not of the scholar.

Ramus seems to have been the first to suggest that algebra deserved
greater importance. For he maintained that algebra underlay certain
parts
of the second and sixth books of Euclid's *Elements,
*as well as the
famous geometrical analysis of the Greek writers.^{39}
That is, long before Zeuthen and Tannery we owe to Ramus the concept of
a geometric algebra of the Greeks. According to Ramus, algebra was only
a vulgar (Descartes later said "barbaric") name for a sort of analytic
mathematics that the Greeks had used; traces of it were to be found, on
the one hand, in Euclid and Pappus and, on the other hand, in
Diophantus.^{40}
Descartes shared this opinion, at least in his *Rules for the
Direction
of the Mind*.^{41}

But the geometrical analysis of the Greeks has its own history.
Largely
lost during the Middle Ages, it reappeared in the sixteenth century, in
particular with Commandino's Latin translation of Pappus' *Mathematical
Collection *and of the works of Archimedes.^{42}
Only toward the end of the sixteenth century did mathematicians gain a
clear picture of the extent of the Greek achievements in the realm of
higher
geometry, and the analytic methods that Pappus pointed to presented the
opportunity at least to emulate these achievements. Mathematicians
began
to search for these analytic methods, and Ramus' suggestion that their
roots lay in algebra was eagerly adopted-by Viète, by Descartes,
and by Fermat.^{43}

But the word "method" (and with the word, the concept) had taken on
a new meaning from Ramus, a new meaning that is reflected in the famous
*Discourse
on the Method *of Descartes. Ramus made method a pedagogical
concept.^{44}
Method was the means of effective teaching; through method, the teacher
brought his students to a profound understanding of the subject matter.
At least, that was the ideal of method. In practice, Ramus' methods
worked
to limit and simplify subjects: accurately transmitting Aristotle's
ideas
and making Aristotle understandable to young students are two different
things. For example, what particularly displeased Ramus about Greek
mathematics
as it stood in the transmitted texts was precisely its rigour, which he
took to be poor method.^{45} The theorems
were
proved, indeed rigorously proved, but they provided neither clarity nor
insight. From such texts, the students learned nothing that could lead
directly to independent activity and achievement in mathematics. Ramus'
answer to this problem was simple, but had a long-range effect. He
represents
the beginnings of the writing of textbooks. In such a textbook of the
seventeenth
century, the *Course in Mathematics *(note the title) of Pierre
Hérigone,^{46}
the *Elements
*themselves are not reprinted, but rather their content
is reformulated pedagogically and recorded for teaching purposes. For
the
sake of good pedagogy, this content is, so to speak, loosed from its
Greek
context and presented in a new form, a new form that assigns to rigour
a less important role than formerly.

What does a philosopher say to this? What does Descartes say? He
writes
in his Second Reply to Objections against the *Meditations*
(1641):

I distinguish two things in the geometric mode of writing, namely the order and the method of demonstration (Analysis, therefore, is not logically rigorous but does have its own sort of rigour. It leads the attentive student to a direct intuition of what has been achieved through analysis. One knows that a result is so because one knows why it is so.ratio demonstrandi). . . . Thereare, moreover, two methods of demonstration, one via analysis and one via synthesis.

Analysis reveals the true way in which a thing was found methodically and, as it were,a priori sothat, if the reader wishes to follow it and pay sufficient attention to everything, he will understand the matter no less perfectly and make it no less his own than if he himself had found it. But it has nothing by which to incite belief in the less attentive or hostile reader. For if he should not perceive the very least thing brought forward, the necessity of its conclusions will not be clear; often it scarcely touches on many things which should be especially noted, because they are clear to the sufficiently attentive reader.

Conversely, synthesis clearly demonstrates, in a way opposite to analysis and, as it were,a posteriori(even though the proof itself is often morea prioriin the former than in the latter), what has been concluded, and it uses a long series of definitions, postulates, axioms, theorems, and problems, so that, if one of the consequents is denied, it may at once be shown to be contained in the antecedents. Thus it forces assent from the reader, however hostile or stubborn. But it is not as satisfying as analysis; it does not content the minds of those wanting to learn, because it does not teach the manner in which the thing was found.

The ancient mathematicians used to employ only synthesis in their writings, not because they were simply ignorant of the other, but, as I see it, because they made so much of it that they reserved it as a secret for themselves alone.

In fact, I have followed in myMeditationsonly analysis, which is the true and best way of teaching....^{47}

We could adduce here similar passages from the works of Viète
*or
*Leibniz,^{48}
but the introduction to the most widely circulated textbook of algebra
in the seventeenth century, the *Key to Mathematics *of William
Oughtred,
probably offers the most conclusive documentation:

When some time ago I served in the family of the recent illustrious Count of Arundel and Surrey to teach each of his children the mathematical disciplines, I composed a certain order of teaching which seemed to me most appropriate to the mathematical mysteries, such that the minds of the students who followed it would be imbued with these sciences not lightly or superficially but intimately and basically. At the request of many learned men, especially the most noble and erudite Lord Charles Cavendish, I first published this order of mine under the title ofHere one has the Cartesian motifs of good pedagogy and of the demonstrative power of analysis, now expressly referred to algebra (as theThe Key to Mathematics.This treatise was not written according to the synthetic method (as is commonly done), by theorems and problems with a wide expanse of words, but according to the analytic way of invention (so that the whole is as a continuous demonstration joined together by the most firm connections), set forth not in words but in the species of things.^{49}

As has been said, this pedagogical motif can be documented on the basis of other examples, and it should not surprise us all that much. One characteristic of the intellectual world of the sixteenth and seventeenth centuries is precisely the extension of the school and university system to include broader segments of society. It would be surprising if this development had not influenced mathematics as the core of any study.

Now what about the second tendency mentioned above, the search for a
universal symbolism? As has been said, this tendency stemmed from the
high
Middle Ages; in the sixteenth and seventeenth centuries, however, it
enjoyed
ever increasing importance. One reason for this may well be the effects
of the invention of printing and the spread of the printed book. What
happened
then was less a question of quantity than of quality, for the printed
book
entailed that man now used his eyes instead of his ears for learning.^{50}
Where one earlier had had to rely on one's memory, one could now spare
that memory. What earlier had to be stored in the brain could now be
found
in the library. We have already pointed to the phenomenon of the
textbook.
Only in a world of the eye could the search for a universal symbolism
yield
mature fruit.

Of what should such a symbolism consist? Listen again to Descartes:

Those things that do not require the present attention of the mind, but which are necessary to the conclusion, it is better to designate by the briefest symbolsSo Descartes speaks in the(nota)than by whole figures: in this way the memory cannot fail, nor will thought in the meantime be distracted by these things which are to be retained while it is concerned with other things to be deduced . . . . By this effort, not only will we make a saving of many words, but, what is most important, we will exhibit the pure and bare terms of the problem such that while nothing useful is omitted, nothing will be found in them which is superfluous and which vainly occupies the capacity of the mind, while the mind will be able to comprehend many things together.^{51}

The universal symbolism desired by Lull or even by Leibniz was
probably
a chimera, but the search for such a symbolism meant that in the
seventeenth
century one would surely be found for mathematics. Roughly put,
mathematicians
were ready to overlook many weaknesses in symbolic algebra-as, for
example,
the lack of total rigour-because this algebra represented at least a
part
of a universal symbolism. In this regard, algebra served as a model. In
his *Essay Concerning Human Understanding, *John Locke, for
example,
said:

They that are ignorant of algebra cannot imagine the wonders in this kind that are to be done by it; and what further improvements and helps, advantageous to other parts of knowledge, the sagacious mind of man may yet find out, it is not easy to determine. This at least 1 believe: that the ideas of quantity are not those alone that are capable of demonstration and knowledge; and that other and perhaps more useful parts of contemplation would afford us certainty, if vices, passions, and domineering interest did not oppose or menace such endeavours . . . . TheLocke, then, serves as a contemporary witness to the transition to a new mode of mathematical thinking. For he knew what algebra was about and where it was headed. It is initially about relations among quantities, but it should also be about relations among other objects of knowledge. With Locke we look into a future whose course is to some extent already determined. A new mode of mathematical thought lies ready to be developed further.relationof othermodesmay certainly be perceived, as well as those of number and extension; and I cannot see why they should not also be capable of demonstration, if due methods were thought on to examine or pursue their agreement or disagreement.^{52}

During the next two centuries a development does take place, which might be called the "algebraicization of mathematics". We see a suppression of intuitive geometry in favour of an abstract algebra. Poncelet and Plucker translate projective geometry into an algebraic form. In the lifetime of one man, Gauss, non-Euclidean geometry moves from its originally geometric, intuitive form into analytic algebraic differential geometry. With each step, the mathematician looses himself from the intuitive physical world and enters into an abstract mathematical world, into a world of structures.

Precisely how this development took place must still be determined.
To start with one will have to be sure about the extent to which it
sprang
from internal tendencies and needs of mathematics. Hans Wussing's
history
of the development of the abstract concept of a group, and Michael J.
Crowe's
study of the emergence of vector algebra, represent examples of such
internal
analysis.^{53} But one may doubt that
historians
will find the whole story within mathematics. Mighty figures, such as
Kant,
to name just one, to some extent opposed such a development. Who or
what
counter-balanced their influence? When even a chemist like Lavoisier
introduces
his *Nomenclature of Chemistry *with the words: "Algebra is the
analytical
method *par excellence; *it was invented to facilitate the
labors
of the mind, to compress into a few lines what would take pages to
discuss,
and to lead, finally, in a more convenient, prompt, and certain manner
to the solution of very complicated questions",^{54}
one may assume that the algebraicization of mathematics did not take
place
in a vacuum, but rather in a continuous, reciprocal interaction with
the
surrounding culture. The precise nature of this interaction awaits the
research of historians.

2. One may cite here as only one example the
concept
of *adaequalitas, *which served as the most important foundation
of
Fermat's method of determining extreme values and tangents to a curve
and
which signified a procedure that was alien to the Ancients.

3. In the Fourth Rule of the then still unpublished
*Regulae
*(composed
ca. 1628) as well as in the Replies to Objections to the
*Meditations
*set out in his correspondence beginning in 1641; see Charles Adam
and
Paul Tannery (eds.), *Oeuvres de Descartes*, X, pp. 376ff
(hereafter,
*AT*) (HR, 1, pp. 12ff).

4. See, in particular, the first book of the *Géométrie
*(Leiden,
1637), where this opinion is repeatedly expressed.

5. See M. S. Mahoney, *The Royal Road: The
Development
of Algebraic Analysis from *1550 *to *1650,
*with Special Reference
to the Work of Pierre de Fermat* (Ph. D., Princeton, 1967), Chapter
III.

6. Thus, for example, John Wallis: "... not only
Archimedes,
but nearly all the ancients so hid from posterity their method of
analysis
(though it is clear that they had one) that more modern mathematicians
found it easier to invent a new analysis than to seek out the old".
Quoted
by T. L. Heath, *History of Greek Mathematics, *Vol. 11* *(Oxford,
1921), p. 21.

7. One might think, for example, of the modern integral calculus or of modern mathematical logic, where complicated processes are often represented symbolically and one in practice computes with symbols according to certain rules.

8. Category theory represents perhaps the newest development in this direction.

9. The decisive breakthrough takes place with the development of non-Euclidean geometry in the nineteenth century and is completed by the axiomatics that arises at the end of that century.

10. In this respect the symbolism of the German and Italian cossists of the late Middle Ages signifies no essential advance; it also consists merely of abbreviations.

11. In P. Tannery, "L'Arithmétique
pythagoricienne",
*Bull.
Sci. Math. *(1885), p. 86; quoted by L. Brunschvicq, *Les
étapes
de la philosophie mathématique *(Paris, 1947), p. 103.

12. The best example is probably Viète's and Descartes' theory of equations. The derivation of the elementary symmetric functions, for example, presupposes (at least historically) the possibility of distinguishing symbolically between unknowns (variables) and constant parameters of an equation.

13. See M. S. Mahoney, "Another Look at Greek
Geometrical
Analysis", *Archive for History of Exact Sciences, *5 (1968),
pp.
318-48; esp. pp. 331-7.

14. Although a couple of theorems of relational
logic
occur in the *Organon, *for example, *syllogismi obliqui, *they
did not belong to the scientific theory of the syllogism, that is, to
analysis.
See I. M. Bochenski, *Formale Logik *(Freiburg/Munich, 1956),
pp.
101-14. Bochenski counts the logic of relations among the achievements
of modern logical research; see *ibid. *p. 434.

15. A. Szabò, *Anfänge der
griechischen
Mathematik *(Munich/Vienna, 1969), Teil III, does not share this
opinion.
But his very arguments for the abstractness, or more exactly the
transition
to abstractness, of Greek mathematics in the fifth century B.C. point
to
a strong dependence on physical experience; for example, in the role of
the physical intuition of motion in the concept of straight lines and
planes.

16. Descartes, *Géométrie, *315ff
(opening of Book II).

17. Viète, *In artem analyticen isagoge*
(Tours, 1591), p. 7: "Quod opus, ut arte aliqua juvetur, symbolo
constanti
& perpetuo ac bene conspicuo datae magnitudines ab incertis
quesititiis
distinguantur, utpote magnitudines quaesititias elemento A aliave
litera
vocali, E, 1, O, V, Y, datas elementis B, G, D, alliisve consonis
designando."

18. See inter alia P. Treutlein, "Die deutsche
Coss",
*Abhandlungen
zur Geschichte der Mathematik, *Heft* *2 (1879), pp. 1-124,
and
J. Tropfke, *Geschichte der Elementar-Mathematik*,* Vol*. II
(Berlin, 1933), Chapter A.

19. *Plethos monadon aoriston*; see P.
Tannery
(ed.) *Diophantus: Arithmeticorum libri sex*, (Leipzig, 1893), 6.

20. *Isagoge*, p. 5: "Logistice numerosa est
quae per numeros, Speciosa quae per species seu rerum formas exhibetur,
ut pote per Alphabetica elements. Logistices speciosae canonica
praecepta
sunt quatuor, ut numerosae ... . Magnitudinem magnitudini addere . . .
. Magnitudinem magnitudini subducere . . . . Magnitudinem in
magnitudinem
ducere . . . . Magnitudinem magnitudini adplicare."

21. Whether and how Descartes was influenced by
his
mathematical predecessors remains unclear. However, the development of
his thoughts about algebra, which can be traced in his *Oeuvres*,
leads to the fairly certain conclusion that the independence he claimed
from Viète was, in fact, the case.

22. *Regulae*, Rule XVI; AT, X, pp. 456ff.
In
the rule itself Descartes employs another symbolism, which is a
transitional
stage between the toss and his ultimate system of *x, y, z*:
unknowns
are designated by small letters, knowns by capitals.

23. *Géométrie*, Book I, pp.
297-300:
"Comment le calcul d'Arithmetique* *se* *rapporte aux
operations
de Géométrie."

24. *Géométrie*, pp. 297ff:
"Ainsi
n'a-t-on autre chose à faire en Géométrie touchant
les lignes qu'on cherche, pour les preparer à être
connues,
que leur en ajouter d'autres, ou en tirer, ou bien en ayant une, que je
nommerai l'unité pour la rapporter d'autant mieux aux nombres,
et
qui peut ordinairement être prise à discretion, puis en
ayant
encore deux autres, en trouver une quatrième, qui soit à
l'une de ces deux, comme l'autre est à l'unite cc qui est le
mime
que la multiplication; ou bien en trouver une quatrième, qui
soit
à l'une de ces deux, comme l'unite est à l'autre, ce qui
est le même que la division; ou enfin trouver une, ou deux, ou
plusieurs
moyennes proportionelles entre l'unité et quelque autre ligne,
ce
qui est le même que tirer la racine carrée ou cubique,
etc.
Et je ne craindrai pas d'introduire ces termes d'Arithmétique en
la Géométrie, afin de me rendre plus intelligible. [So
too
in geometry, to find required lines it is merely necessary to add or
subtract
other lines; or else, taking one line which I shall call unity in order
to relate it as closely as possible to numbers, and which can in
general
be chosen arbitrarily, and having given two other lines, to find a
fourth
line which shall be to one of the given lines as the other is to unity
(which is the same as multiplication); or, again, to find a fourth line
which is to one of the given lines as unity is to the other (which is
equivalent
to division); or finally, to find one, two, or several mean
proportionals
between unity and some other line (which is the same as extracting the
square root, cube root, etc. of the given line). And I shall not
hesitate
to introduce these arithmetical terms into geometry, for the sake of
greater
clearness." [(D. E. Smith and M. L. Latham (trans), *The Geometry of
René Descartes* (New York, 1954), pp. 2-5)] Particularly
important
here is the last sentence, which shows clearly that Descartes was
aiming
not at the arithmetization of geometry, but rather at an
algebraicization
of geometry.

25. *Algebra, or the Doctrine of Equations*
was,
for example, the title of a work by Richard Balam, published in London
in 1650 and 1653.

26. *Géométrie*, Book Ill, p.
380:
"Au reste tant les vraies racines que les fausses ne sont pas toujours
réeles mais quelquefois seulement imaginaires; c'est à
dire
qu'on peut bien toujours en imaginer autant que j'ai dit en chaque
équation;
mais qu'il n'y a quelquefois aucune quantité, qui corresponde
à celles
qu'on imagine." [Neither the true nor false roots are always real;
sometimes
they are imaginary; that is, while we can always conceive of as many
roots
for each equation as I have already assigned, yet there is not always a
definite quantity corresponding to each root so conceived of.] [D. E.
Smith
and M. L. Latham (trans), op. cit. p. 175)]

27. To be sure, one finds already in the sixteenth century solutions that contain the root of a negative number, but precisely as solutions of particular individual equations. Descartes makes "imaginary" solutions general and in fact establishes them on structural grounds.

28. See J. Klein, *Greek Mathematical Thought
and
the Origin of Algebra* (Cambridge, Mass., 1968).

29. See Ch. Henry and P. Tannery (eds), "Analytica
eiusdem methodi [de maxima et minima] investigatio", *Oeuvres
de Fermat, Vol*. I (Paris, 1891), pp. 147-53, where the essay is
reproduced under the title "De maxima et minima".

30. See letter to Brulart de St.-Martin, 31.
III[?].
1643, C. Waard (ed.), *Oeuvres, Supplement*, Paris, 1922, pp.
120-5.

31. In *De aequationum localium transmutatione
et
emendatione ad multimodam curvilineorum inter se vel cum rectis
comparationem,
cui annectitur proportionis geometricae in quadrandis infinitis
parabolis
et hyperbolis usus*,
*Oeuvres*, I, pp. 255-85. The title appears
to have arisen from a conscious borrowing from Viète's works on
the theory of equations, *De aequationum recognitione et emendatione
tractatus duo* (composed ca. 1593, publ. Paris, 1615, and Leiden,
1646).

32. On the concept of *epistêmê*
in early Greek mathematics, see P.-H. Michel, *De Pythagore à
Euclide* (Paris, 1950), p. 22.

33. See M. S. Mahoney, "Another Look at Greek
Geometrical
Analysis", *op. cit.*

34. Fermat (at least where he proceeds algebraically) and Descartes are outstanding examples of this.

35. In addition to Descartes (see below),
Viète,
*Isagoge*,
Chapter VI and Marino Ghetaldi, *De resolutione et compositione
mathematica*
(Rome, 1630), I, pp. 1ff.

36. On this subject, see W. J. Ong, *Ramus:
Method
and the Decay of Dialogue* (Cambridge, Mass., 1958).

37. On this subject, see P. Rossi, *Clavis
Universalis*
(Milan/Naples, 1960).

38. Beginning in the mid-fifteenth century there are exceptions to this rule, in particular at various German universities. By and large, however, algebra developed outside the universities, and the history of its introduction into the university curriculum remains as yet undetermined.

39. For example, Ramus, in his *Geometriae
libri
septem et viginti* (Basel, 1569), p. 6 (of the Frankfurt, 1627,
edition),
sets out the algebraic content of Euclid, 11, 4 - (a + b)^{2} =
a^{2} + b^{2} + 2ab - by means of a numerical example
and
then remarks, ". . . hic geometriae analyseos usus superest".

40. Ramus, *Scholarum mathernaticarum libri
unus
et triginta* (Paris, 1569; Frankfurt, 1627), Book 1, 35: "Sed ex
his,
quorum scripta superant, praecipuus est Pappus: . . . Diophantus cujus
sex libros, cum tamen author ipse tredecim polliceatur, graecos habemus
de arithmeticis admirandae subtilitatis artem complexis, quae vulgo
Algebra
arabico nomine appellatur: cum tamen ex authore hoc antiquo (citatur
enim
a Theone) antiquitas artis appareat."

41. See *Regulae*, Rule IV; *AT*, X,
pp.
376ff (HR, I, pp. 12ff).

42. Pappus (Pisa, 1588, edition) thereafter counted among the most widely read classical texts. It served, for example, as point of departure (and even as initial stimulus) for several of Fermat's investigations.

43. See M. S. Mahoney, *Royal Road*, Chapter
Ill.

44. See W. J. Ong, *Ramus*, Chapter VII, XI.

45. Thus Ramus in Book Ill of his *Scbolae
mathematicae*
often takes Euclid severely to task for the poor method of the *Elements*.

46. Four volumes in three publications (Paris, 1634-37); and Supplement (Paris, 1642).

47. AT, VII, p. 155 (HR, II, pp. 48-9).

48. The pertinent passages for Leibniz would be
those
concerning his *characteristica universalis.*

49. William Oughtred, *Clavis mathematicae
denuo
limata sive potius fabricata *(Oxford, fifth edition, 1693),
Introduction
(added to third edition). Oughtred then goes on to speak of the
usefulness
of algebra in understanding Euclid, Archimedes, Apollonius, and
Diophantus
and in solving the most difficult problems.

50. W. J. Ong's interpretation of Ramist thought is based in part on this transition from ear to eye.

51. *Regulae, *Rule XVI; AT, X, p. 454 (HR,
1,
p. 66).

52. John Locke, *Essay of Human Understanding *(1690),
quoted by H. J. Kearney, *Origins of the Scientific Revolution *(London,
1965), pp. 131ff.

53. Berlin, 1969, and South Bend, Ind., 1967.

54. Quoted by C. C. Gillispie, *The Edge of
Objectivity
*(Princeton,
1960), p. 245.