# Post hoc ergo propter hoc vs Cum hoc ergo propter hoc

I am trying to write an essay and would like to use a saying for "Because Event B is during Event A, Event B is related/caused by Event A." I have in mind

Post hoc ergo propter hoc

and

Cum hoc ergo propter hoc

I recall hearing both quotes but am having trouble differentiating them. Keep in mind, I have almost no prior Latin experience.

The more common one, I think, is post hoc ergo propter hoc, sometimes just "post hoc fallacy." It's translated to, "After this therefore because of this." It's used when someone tries to establish causality even when there is no real evidence to support it.

The other one is cum hoc ergo propter hoc, which actually I've not heard of in Latin. It is translated as, "With this therefore because of this." The typical thing I hear is "correlation does not equal causation. The fallacy here is that just because two things correlate, they might not be related at all, as Spurious Correlations so brilliantly shows.

They're very similar, but differ on viewpoint orientation. Examples:

I switched from whole milk to 2% and my child scored an A on their last test after making C's.

This would be post hoc fallacy. It states that switching from 2% caused this one event. It does not posit a relationship between intake of milk and grades, though. The act of switching did that. For any child who switches to 2%, you should imagine an immediate grade boost on the text.

The more 2% milk my child drinks, the smarter he becomes.

This falls under the "correlation != causation" problem, since a relationship between drinking 2% and getting better grades is posited.

If you're charting this (no time to chart right now, sorry), the increase of 2% and the child's IQ would both increase or decrease together.

For post hoc fallacy, you should see a flat line (or so) until the act of switching to 2%, where then you should see a spike.

Hope that clarifies.

• My impression was that the OP was asking about contemporaneity, not correlation, which is slightly different. – brianpck Mar 15 '17 at 11:54
• @brianpck Can you explain further? I got correlation from "related to/caused by Event B". – cmw Mar 15 '17 at 12:00
• The two are really related, but distinct in my mind. A "correlation" fallacy would say something like, "Everyone with blond hair is kind, ergo" whereas a "contemporary" fallacy would say, "I choked while eating steak, ergo." Not sure if I am grasping at straws here... – brianpck Mar 15 '17 at 13:12
• @brianpck I'm no expert in logical fallacies, but the latter would sound like a post hoc fallacy, no? "I choked on eating steak, ergo steak causes choking." At least, that's how I would interpret it. I could very well be wrong, though. – cmw Mar 15 '17 at 13:15