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-logy is a suffix in the English language, used with words originally adapted from Ancient Greek language ending in -λογία (-logia).[1] The earliest English examples were anglicizations of the French -logie, which was in turn inherited from the Latin -logia.[2]

It has two main senses in English[3]:

  • a combining form used in the names of sciences or bodies of knowledge (e.g. theology or sociology)
  • the root word nouns that refer to kinds of speech, writing or collections of writing (e.g. eulogy or trilogy)



In words of the type theology, the suffix is derived originally from -λογ- (-log-) (a variant of -λεγ-, -leg-), from the Greek verb λέγειν (legein, "to speak").[4] The suffix has the sense of "the character or department of one who speaks or treats of [a certain subject]", or more succinctly, "the study of [a certain subject]".[5]

In words of the type trilogy, the "-logy" element is derived from the Greek noun λόγος (logos, "speech").[4] The suffix has the sense of "[a certain kind of] speaking or writing".[6]

-logy versus -ology

In English names for fields of study, the suffix -logy is most frequently found preceded by the euphonic connective vowel o so that the word ends in -ology.[7] In these Greek words, the root is always a noun and -o- is the combining vowel for all declensions of Greek nouns. However, when new names for fields of study are coined in modern English, the formations ending in -logy almost always add an -o-, except when the root word ends in an "l" or a vowel, as in these exceptions:[8] analogy, dekalogy, disanalogy, genealogy, genethlialogy, herbalogy (a variant of herbology), idealogy (a misspelling of ideology), mammalogy, mineralogy, paralogy, pentalogy, petralogy (a variant of petrology), tetralogy; elogy; antilogy, festilogy, trilogy; palillogy, pyroballogy; dyslogy; eulogy; and brachylogy.[6] Linguists sometimes jokingly refer to haplology as haplogy (subjecting the word haplology to haplology).

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