Contemporary philosophers have exercised themselves with the problem of our knowledge of other minds. Enmeshed in the dogma of the ghost in the machine, they have found it impossible to discover any logically satisfactory evidence warranting one person in believing that there exist minds other than his own. I can witness what your body does, but I cannot witness what your mind does, and my pretensions to infer from what your body does to what your mind does all collapse, since the premises for such inferences are either inadequate or unknowable.

Ch. II: Knowing How and Knowing That, (10) Solipsism - The Concept of Mind (1949)