Does "All" imply one or more?

Solution 1:

It certainly implies that there are at least two books (because it's plural), although logically and semantically speaking, it is possible for there to be no books at all (or just one).

It's not ambiguous, unless either:

• the person making the statement has already made it clear, or makes it clear immediately afterwards, that he/she doesn't know if there are any books, but if there were, they would be red, or
• it is deliberately said in a "can you figure out the trick in this problem?" or similar method in an attempt to confuse someone.

Solution 2:

It would depend on the context.

A logician or computer programmer would probably not infer that there are a non-zero number of books. A computer programmer would probably want to know if there can be zero or one books (and accept any of the possible answers as sensible).

In normal speech, it tends to imply that there are at least two books - it would be surprising if there were fewer than two, but you couldn't complain that the statement was strictly inaccurate.

Solution 3:

Depending on context, I could say "I want you to hand over all your books" without knowing whether there were zero, one or more books. But It wouldn't make sense to say "all the books were red" if no books were handed over :-)