What is the Latin word for theory?

The usual Latin words for “theory” are ars, artificium, doctrīna; also praeceptum, ratiōcinātiō, prācticus. The right choice depends on the sense; see the distinctions below.

English → Latin

“theory” in Latin

arsart, skill, craft, handicraft; trade, occupation, employment; cunning, artifice, fraud, stratagem artificiumart, craft, skill, talent, artifice, craftsmanship; profession, trade, an employment doctrīnateaching, instruction; learning, erudition; doctrine, theory praeceptumteaching, lesson; precept; order, command ratiōcinātiōreasoning, ratiocination prācticuspractical; active

The English word theory itself goes back to Latin theōria.

Riddle & Arnold A Copious and Critical English–Latin Lexicon, 1864

theory

ars (the fundamental principles of an art or science; Vid: Auctor ad Her., 1, 2, 3; Cic., De Or., 2, 27, 30; then, both in sing. and plur. = the rules of art; also a book of instruction; Vid: Cic., Brut., 12, 48; Quint., 2, 15, 4, Spald., and 18, 1, 15, Frotsch.): artificium (system; an art or science; Vid: Cic., De Or., 1, 32, 146, and 2, 19, extr.); doctrina: praecepta, -orum, plur., (The words are found in this connection and order.) ars et praecepta (the principles or rules of an art or science; Vid: Cic., De Or., 2, 11, in.): ratiocinatio (Vitr., 1, 1; opposed to fabrica, the scientific knowledge that can explain and justify its works on the principles of architecture). To construct a theory, artem componere: a moral theory, conformatio officiorum (Cic., Fin., 5, 6, 15): theory and practice, ratio atque usus: to combine theory with practice, doctrinam ad usum adjungere: you must combine theory with practice, discas oportet et quod didicisti agendo confirmes: to refer anything to a theory, aliquid ad rationem revocare, or ad artem et praecepta revocare: it is not enough to know the theory of virtue, without putting it in practice, nec habere virtutem satis est, quasi artem aliquam, nisi utare.

Quick answer

What is the Latin word for theory?: The usual Latin words for “theory” are ars, artificium, doctrīna; also praeceptum, ratiōcinātiō, prācticus. The right choice depends on the sense; see the distinctions below.

Entry from J. E. Riddle & T. K. Arnold, A Copious and Critical English–Latin Lexicon (rev. C. Anthon, New York: Harper, 1864), digitised by Fergus J. P. Walsh, CC BY-SA 4.0; Latin markup adapted by latindictionary.co.