-logy is a suffix in the English language, used with words originally adapted from Ancient Greek ending in , which was in turn inherited from the Latin. The suffix became productive in English from the 18th century, allowing the formation of new terms with no Latin or Greek precedent. The English suffix has two separate main senses, reflecting two sources of the -λογία suffix in Greek:
theology or sociology. In words of the type theology, the suffix is derived originally from -λογ- , from the Greek verb λέγειν. The suffix has the sense of "the character or deportment of one who speaks or treats of ", or more succinctly, "the study of ".
the root word nouns that refer to kinds of speech, writing or collections of writing, e.g.
eulogy or trilogy''. In words of this type, the "-logy" element is derived from the Greek noun λόγος. The suffix has the sense of " speaking or writing".Philology is an exception: while its meaning is closer to the first sense, the etymology of the word is similar to the second sense.
-logy versus -ology
In English names for fields of study, the suffix -logy is most frequently found preceded by the euphonic connective vowelo so that the word ends in -ology. 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 -logyalmost always add an -o-, except when the root word ends in an "l" or a vowel, as in these exceptions: analogy, dekalogy, disanalogy, genealogy, genethlialogy, herbalogy, mammalogy, mineralogy, paralogy, petralogy ; '; antilogy, '; trilogy, tetralogy, '; ', '; '; eulogy; and brachylogy. Linguists sometimes jokingly refer to haplology as haplogy.
Additional usage as a suffix
Per metonymy, words ending in -logy are sometimes used to describe a subject rather than the study of it. This usage is particularly widespread in medicine; for example, pathology is often used simply to refer to "the disease" itself rather than "the study of a disease". Books, journals, and treatises about a subject also often bear the name of this subject. When appended to other English words, the suffix can also be used humorously to create nonce words. As with other classical compounds, adding the suffix to an initial word-stem derived from Greek or Latin may be used to lend grandeur or the impression of scientific rigor to humble pursuits, as in cosmetology or cynology.
