C++ FAQ Celebrating Twenty-One Years of the C++ FAQ!!!
(Click here for a personal note from Marshall Cline.)
Section 19:
[19.2] When would I use inheritance?

As a specification device.

Human beings abstract things on two dimensions: part-of and kind-of. A Ford Taurus is-a-kind-of-a Car, and a Ford Taurus has-a Engine, Tires, etc. The part-of hierarchy has been a part of software since the ADT style became relevant; inheritance adds "the other" major dimension of decomposition.