[Russell] Subsist vs Exist

So I’m reading Russell’s On Denoting and I come across this passage:

The problem is that when I earlier looked up “subsist” in the OED I found:

When I looked up “exist”:

…and I came to the conclusion that subsist and exist are essentially synonyms. Silly me!

So what’s up? What’s the difference? I’m assuming it’s some obscenely nuanced difference which you could only find in the Philosophy of Language (he said bitterly).

Oh, I should add that Russell has an endnote where he says that he considers “subsistence” and “being” to be synonymous.

I assume it’s a nuance-- there IS a difference between exist and subsist, namely the ‘sub’ part, suggesting it’s predicated on something else rather in its own right. You might want to look at the etymology section of the OED for each and see what the old old difference is (like “to stand apart from” versus “to stand under” like “sub-stance,” “sub-strate” etc, which all imply a place in a hierarchy).

Oh, looking at OED, there is an older simple definition, “To have its being or existence in a certain manner, form, or state, or by a certain condition”-- so it is an issue of predication or condition.