The difference is that using methods from some other class (say car) by inheritance means that the class (say racing car) is a kind of that other class (a racing car is a car). While using means that a class (say racing car) is using methods from some other class (say engine) without being of that kind of the other class (a racing car has an engine but is not an engine). This argument is probably not C++ specific but that is where I remember it from.