My professor has asked us to give a substantive presentation in order to complete a course. I needed to look up the dictionary as this was a new word for me. Dictionaries do not point to a clear difference between substantive and substantial. How do these words differ in terms of the usage? Their etymology is the same, so this is a matter of usage, I guess.
Beyond the dictionary definitions, something that is
must have some substance to it, must not be trivial, must be meaningful. It is probably not simply pithy (on the short side), but still needs some support.
Something that is
needs bulk to it (in comparison).
That is, in quantity, 'substantial' is more than 'substantive', but substantive is not brief.
Another way to say this is that 'substantial' is a lot, and substantive has been filled out.
I think there's an emerging difference in usage. By dictionary definitions, both words have a range of meanings, with considerable overlap.
Google's first three entries for substantial cover most usages today 1: Of considerable importance, size, or worth. 2: Strongly built or made. 3: (of a meal) Large and filling.
Their first two entries for substantive are 1: Having a firm basis in reality and therefore important, meaningful, or considerable. 2: Having a separate and independent existence.
Here's a chart showing how substantive has crept up in recent decades.
I'll just throw in an OED definition for substantiate - To demonstrate or verify by proof or evidence. I believe that increasingly, substantive is used to mean capable of being substantiated.
TL;DR: Substantial today tends to refer to physical attributes; substantive is less common overall, and is more likely to be used metaphorically (of abstract concepts).