What is the origin/formal definitions of the phrase "pros and cons"?

The phrase "pros and cons" is often used to weigh the positive and negative effects that would result from taking a particular course of action. When trying to explain to someone else why only actions (and not objects or people's reasons for doing things) have pros and cons [e.g. there are no pros or cons for grass; there are pros and cons for having grass], I realized that I have no idea why this seems to be the rule.

I have so far come to the conclusion that both "pro" and "con" are probably abbreviations, but I can't figure out what they are abbreviations of. Does anyone know? How does this create the usage rules detailed above?

Solution 1:

Pro is not an abbreviation, but 'con' is for 'contra.' From the OED:

An argument or consideration in favour of something; reasoning in support of a proposition, thesis, etc. Chiefly in pros and cons (also pros and contras): reasons or arguments for and against something, advantages and disadvantages. Occas. also pro and contra (also pro and con): argument, debate.

And the etymology of 'pro'

Etymology: < classical Latin prō (preposition) before (of place), in front of, for, on behalf of, instead of, in return for, on account of, etc. < the same Indo-European base as ancient Greek πρό forward, before, in front of, earlier than, Sanskrit pra- forth, Early Irish ro- , prefix forming the perfect tense, Gothic fra- , verbal prefix (see discussion at for- prefix1), ultimately showing an ablaut variant of the Indo-European base of fore adv. In English use chiefly after pro and contra at pro adv. 1a and related uses of pro adv.

Arguably 'pro' could be considered an abbreviation for 'prove' in this specific idiom as evidenced by earlier usages of the idiom such as Letters and Papers of J. Shillingford:

The Bysshoppis Court what court he hadde and sholde have, here of was right moche longage and reson prove and contra.

From my own knoweldge of Latin I'd say the phrase 'pro et contra' might mean 'for and opposing' or 'for and against' which means that the translation of the roots is almost identical to the modern understanding of the idiom.

Solution 2:

The phrase ‘pros and cons’ is an abbreviation of the Latin phrase pro et contra, ‘for and against’, and has been in use in the abbreviated form since the 16th century, according to the Oxford Dictionary Online.