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The argument is not valid because it incorrectly uses the logical structure In the chain

A-B-m-C

"all" (A to B) should precede "most" (B to C) for a valid conslusion. Here the argument starts with "all" and then uses "most" which does not allow for a valid conclusion to be drawn. The transition from "most" to "some" is not logically sound in thi context, as it doesn't guarantee that any specific group (violonists at the New York Philharmonic) fits the conclusion.