The Generalist

Weekly Word: A priori

The weekly word is back! Once a week I will define and/or explore a new word in the search for more precise meaning in the English language.

A priori is a Latin term that I use quite often in the articles I post on this site. It didn’t occur to me at first to do a Weekly Word for it, probably because there was no question in my mind as to what it meant, but now I think rather than explaining it in every article or post, I will just link back here!

I first encountered this term in Ludwig von Mises’ great work Human Action. Before that time I had never heard of it and it actually took some time and discussion before I fully understood what it meant. Hopefully, this post will help bring you up to speed quicker.

Here is what Percy L. Greaves, Jr. has to say in his very helpful glossary of words used in Mises’ Human Action, Mises Made Easier:

A priori, (Latin). Literally, from the former or preceding. Self-evident knowledge known by reason alone without any appeal to experience or sensory perceptions. Nonempirical. Opposed to a posteriori (q.v.).

An a priori statement is one which the human mind can neither question nor contradict and which cannot be further analyzed, diagnosed, broken down or traced back to a logically prior cause. It is thus the original datum or premise which forms the starting point for deductive reasoning.

That’s actually a very good definition, but if you’re new to logic it might not make sense, so I’ll give you a few examples.

  • I think therefore I am.
  • 2+2=4
  • The square of the hypotenuse of a right triangle is equal to the sum of the squares of the other two sides.

All of the deductive reasoning that follows from an a priori statement is also a priori (it is implied in the original statement) and is logically certain. This is in contrast to scientific knowledge, (also known as empirical, inductive, or a posteriori) which is never certain.

Some things that are a priori may surprise you. This is because even though technically all the new information you learn when you reason deductively is implied by the original statement, this does not mean doing the actual reasoning is easy. Take the Pythagorean theorem above for instance. Some of you may have difficulty just following what’s going on when it’s explained to you. Imagine what Pythagoras had to do!

Economics is a body of a priori knowledge. This no doubt will surprise a lot of you. The concept of Natural Rights is also a priori. Properly defined, so is all of ethics.

Want to know more? The following great works may be of interest to you:


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