What is the difference in meaning between the postposition "causa" and the preposition "propter"? Both mean "because", right?
The difference between causa and propter is that
- propter refers to an existing objective cause or motivation for something;
- causa refers to an intended purpose of an action, to be realised in the future. You can perhaps translate it as "for the sake of."
For example, you say exempli causa, meaning "to serve as an example, for instance." You don't say propter exemplum, or, if you do, it means "because of some example (that was given earlier)." Causa is also frequently used with possessives, like mea, tua, vestra, nostra causa etc., "for my, your, our sake."
On the other hand you say propter timorem signa ferre nolebant, "they would not bear the standards out of fear." You would not say timoris causa.
But I should note that the distinction is not always clear and is not strictly adhered to at all times.
Note: causa is not a postposition, it is simply a noun in the ablative, and while it is very regularly found in second position, there are exceptions to that rule.