a priori

[bill888]

where did the term 'a priori' originate?

[Quizmonster]

From Latin, where the words mean...'a' = from...'priori' = preceding. It is a legal term applied to reasoning from what is logically or chronologically prior. You hear it in such sentences as: "There is an a priori case against him."

[bernardo]

I have only ever heard the term "a priori" in the subject of languages - an a priori language is one derived from other parent languages (e.g. Italian derived from Latin), compared with a posteriori languages whose sords are not derived from others (e.g. Solresol).

The phrase I would expect in the context mentioned by Quizmonster is "prima facie" (i.e. on the face of it, on first appearances) but of course there is no possibility that the great Q might have got muddled up between two different things.

[bernardo]

Whoops - I meant the other way round (a priori - Solresol and a posteriori - Italian).

[Quizmonster]

You're wrong, Bernardo. You see, I did get muddled between the exact two phrases you list! (My apologies to you, therefore, Bill.)

However, 'a priori' does not just have to do with languages. It refers to reasoning from cause to effect or what we might normally call 'thinking deductively'. That is, one considers situations in accordance with one's existing knowledge but before carrying out any investigation into the specifics of the actual case. It may well be, therefore, that the examination reveals one's early conclusions were mistaken.

[Hgrove]

As far as I know if you say a priori it means you are pre-judging a situation whereas a posteriori means judging the situation after the event.  I had mainly heard these expressions in connection with moral judgments on ethical issues.

[Quizmonster]

Absolutely, HG. One is prejudging legal or ethical situations, but based on what one already knows.

There is a suggestion that British juries might in future be told of an accused's previous convictions for similar offences. So, if a man has been found guilty of molesting little girls three times before, the jury might feel that was good a priori evidence that he is also guilty of child-molestation this time. That need not be so, however...only an examination of the specific evidence being offered now will show his current guilt or innocence.

As I said in my second answer above - despite offering a poor example in my first - this is deductive or a priori reasoning. And - though seemingly 'logical' in many minds - it's not always right, of course.