In all the texts I have seen on differential algebra, differential rings/fields/algebras/etc. are always specified as having a *finite* number of derivations (some books e.g. those specifically on differential Galois theory, even introduce the differential rings/etc. as having only a single derivation). I am somewhat confused why the finite restriction is hammered in place.

There are a few results in Kolchin's book that are proved using induction on the number of derivations. There is also at least one proof I could find while skimming back that uses a matrix over a vector space whose basis is the set of derivations. But as for the induction proofs, they could probably still work through some careful application of abstract nonsense or transfinite induction. I'm not terribly familiar with the logistics of infinite matrices, but perhaps the matrix proof(s) would still work by considering those.

More than anything though, the results that are proved in this fashion seem to be quite few in between. It seems like the vast majority of results could be extended to the infinite case, and then one could simply add in the other theorems as special cases that only apply to "finite-partial" differential rings.

Is it simply a problem of few applications of rings/etc. with an infinite set of derivations? Or is there some very important result that actually doesn't hold in "infinite-partial" differential rings, that makes studying them unfruitful? Or is there actually a body of research in this direction that I simply am not aware of?