The Difference Between Ex-Ante, Post Hoc, Ex Post, A Priori, and A Posteriori
If you do a lot of (good) reading you have probably run into a few highbrow, Latiney sounding phrases like those in the title of this post.
I’m guessing you almost looked them up several times, but if you’re here you finally did. Well done. Here they are.
- Ex Ante means before the event, and is basically a prediction of something. In the financial world it’s often a prediction of a return on an investment.
- Ex Post means after the event, and means something that is settled after the event actually happens. For investment companies it’s a look back at how they company actually did as opposed to how well they planned on doing.
- A Priori means from earlier, and refers to knowledge we have naturally, obviously, or before (and not requiring) testing or experience.
- A Posteriori means from the latter, and refers to knowledge we must acquire by testing or evidence.
- Ad Hoc means for this, and indicates something designed for a specific purpose rather than for general usage.
- Post Hoc means after this, and refers to reasoning, discussion, or explanation that takes place after something has already transpired.
- i.e. comes from id est in Latin, basically meaning it is, and signifies a restatement of what was just said. It’s a reiteration, not an example or case in point.
- e.g. comes from exempli gratia in Latin, which means “for example”. So if you make a point and then say, e.g., you don’t want to restate your point, you want to provide an instance of that being true.
Discussion
I’ve been guilty of mangling these in the past as well.
It’s strange how people incorporate obscure language into their repertoire without knowing what it means, and I find that outside of deeply intellectual (both pseudo and legitimate) circles, these terms are almost always misused.
The one that surprised me most was ad hoc, which I more thought of as meaning “without a plan”, as opposed to being “custom for this situation”. The relationship between those two, and the fact that they’re likely to be coincident, is interesting by itself.
The most common terms you’ll encounter in scientific reading are a priori and a posteriori, which deal with the two types of knowledge:
- That which you know without experience or experiment (a priori)
- And that which you can only know after you gather evidence (a posteriori)
The distinctions between i.e. and e.g. are less exotic and are part of common grammar at this point, but many still confuse them.
I hope this has been helpful.