Sentence:  I repeat: it suffices that a <WSD>book</WSD> be possible for it to exist. Only the impossible is excluded. For example: no <WSD>book</WSD> can be a ladder, although no doubt there are <WSD>books</WSD> which discuss and negate and demonstrate this possibility and others whose structure corresponds to that of a ladder. 
Meaning of the word marked with <WSD> tags:  A collection of sheets of paper bound together to hinge at one edge, containing printed or written material, pictures, etc.