"Composition" is a word that can mean several things, and without having read the original source I never really understood which version they mean. As a rule, I've always viewed "composition" as "gluing together things that don't know necessarily know about each other", and that definition works well enough, but that doesn't necessarily eliminate inheritance. So then I start thinking in less-useful, more abstract de…
It's that broader version of composition—particularly in its extreme realization, delegation—that underlies a lot of the behavioral patterns in the book. For example, the State and Strategy patterns boil down to "this object relies on another object to fill in the behavior here, and there are ways to choose what that other object is", which is something it's easy to arrange with subclassing and the only point of the pattern is to avoid subclassing.