Where can I read about objections to the validity of a question such as "the purpose of life" where the question baselessly presupposes that life HAS a purpose. And more broadly, even if it claimed that EVERYTHING has a purpose, how can such a claim be justified? It seems that many metaphysical questions suffer from this lack of validity due to unfounded presuppositions or assertions. Where can I read about this as applied to philosophical questions in general? Thank you.

I recommend the essays in Part Three ("Questioning the Question") of E.D. Klemke's collection The Meaning of Life (Second Edition). If I may also mention my own short article on one aspect of this topic, you can find it at this link.

The literature on whether philosophical questions in general rest on false presuppositions is enormous. You might start with this SEP article (especially section 4.1). There's also a growing literature on whether metaphysics in particular (and ontology more particularly) concerns mostly pseudo-questions; see, for example, this collection.

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