[gboyer]

You can just do both, though. Use interfaces for polymorphism, to define the interactions between your objects -- and then, if you want, use inheritance as one possible strategy for code reuse.

[colomon]

That works great if you're only using one interface in your class. What if you need to include two?

[gboyer]

Then you use a different reuse strategy, like composition. The language is not ideal in this regard, certainly.