Etymology
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logic (n.)

mid-14c., logike, "branch of philosophy that treats of forms of thinking; the science of distinction of true from false reasoning," from Old French logique (13c.), from Latin (ars) logica "logic," from Greek (he) logike (techne) "(the) reasoning (art)," from fem. of logikos "pertaining to speaking or reasoning" (also "of or pertaining to speech"), from logos "reason, idea, word" (see Logos). Formerly also logick. Sometimes formerly plural, as in ethics, but this is not usual. Meaning "logical argumentation" is from c. 1600. Contemptuous logic-chopper "sophist, person who uses subtle distinctions in argument" is from 1846.

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logician (n.)
"person skilled in logic," late 14c., from Old French logicien (13c.), from logique (see logic). The Greek word was logistes.
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physicological (adj.)

"pertaining to logic as illustrated by physics," 1704, from physicologic "logic illustrated by physics," from physico- + logic. Related: Physicologic; physicologically.

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logical (adj.)
early 15c., "based on reason, according to the principles of logic," from logic + -al (1). Meaning "pertaining to logic" is c. 1500. Attested from 1860 as "following as a reasonable consequence." Related: Logically. Logical positivism, in reference to the ideas of the Vienna Circle of philosophers, is from 1931.
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*leg- (1)

Proto-Indo-European root meaning "to collect, gather," with derivatives meaning "to speak" on the notion of "to gather words, to pick out words."

It forms all or part of: alexia; analects; analogous; analogue; analogy; anthology; apologetic; apologue; apology; catalogue; coil; colleague; collect; college; collegial; Decalogue; delegate; dialect; dialogue; diligence; doxology; dyslexia; eclectic; eclogue; elect; election; epilogue; hapax legomenon; homologous; horology; ideologue; idiolect; intelligence; lectern; lectio difficilior; lection; lector; lecture; leech (n.2) "physician;" legacy; legal; legate; legend; legible; legion; legislator; legitimate; lesson; lexicon; ligneous; ligni-; logarithm; logic; logistic; logo-; logogriph; logopoeia; Logos; -logue; -logy; loyal; monologue; neglect; neologism; philology; privilege; prolegomenon; prologue; relegate; sacrilege; select; syllogism; tautology; trilogy.

It is the hypothetical source of/evidence for its existence is provided by: Greek legein "to say, tell, speak, declare; to count," originally, in Homer, "to pick out, select, collect, enumerate;" lexis "speech, diction;" logos "word, speech, thought, account;" Latin legere "to gather, choose, pluck; read," lignum "wood, firewood," literally "that which is gathered," legare "to depute, commission, charge," lex "law" (perhaps "collection of rules"); Albanian mb-ledh "to collect, harvest;" Gothic lisan "to collect, harvest," Lithuanian lesti "to pick, eat picking;" Hittite less-zi "to pick, gather."

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metalogical (n.)

"beyond the sphere of logic, transcending logic," by 1865; see meta- in the third sense of "transcending, overarching, dealing with the most fundamental matters of" + logical. Related: Metalogic (n.), by 1842; metalogical.

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thematic (adj.)
1690s, in logic, from Greek thematikos, from thema (genitive thematos; see theme). From 1871 of writing or discourse. Related: Thematical; thematically.
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analytics (n.)
the division of logic which distinguishes good from bad arguments, 1590s, from Latin analytica from Greek analytika, from stem of analyein "unloose, release, set free," from ana "up, back, throughout" (see ana-) + lysis "a loosening," from lyein "to unfasten" (from PIE root *leu- "to loosen, divide, cut apart"); also see -ics. Ta Analytika was the name of Aristotle's treatises on logic.
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declassify (v.)

1865, originally a term in logic; with reference to state secrets, 1946; from de- + classify. Related: Declassified; declassifying; declassification.

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illogical (adj.)
"without sound reasoning according to rules of logic," 1580s, from assimilated form of in- (1) "not, opposite of" + logical. Related: Illogically.
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