Hume claims that there are some “philosophical” ideas for which it is “impossible to assign” any “impression [from which] that supposed idea derived.” Does this contradict anything he said earlier...

Hume claims that there are some “philosophical” ideas for which it is “impossible to assign” any “impression [from which] that supposed idea derived.” Does this contradict anything he said earlier about all the ideas in our minds? How do you think Hume would answer you if you objected that his claim about philosophical ideas contradicts what he said earlier about all ideas?