This definition bothers me immensely, because it can tempt people to make argumenta ad lapidem against idealism. Yet "idealist" philosophers can superficially f

This definition bothers me immensely, because it can tempt people to make argumenta ad lapidem against idealism. Yet "idealist" philosophers can superficially fit the criterion of "believing that reality is mentally constructed" but not believe that things only exist in so far as they are perceived, as Berkeley did, and that someone might just walk through walls if they really want it so. Specially because certain words have no uniform usage among philosophers Kant for example, might be said to have believed that "reality" was "mentally constructed", and he used a really similar language in describing how we perceive the world. But he also wrote quite clearly that Berkeley's idealism was absurd and that we can never perceive anything which violates physical laws. And together with denying the possibility that we might ever come to real knowledge of the world by thinking alone, that was the whole point of his "transcendental idealism".