{ 1 } - we have no knowledge of the thoughts and feelings of others.
{ 2 } - statements about the thoughts and feelings of others can be translated into statements about their behavior.
{ 3 } - we can know what others think or feel by a special intuition of their inner states.
{ 4 } - facts about behavior can be evidence for beliefs about the thoughts and feelings of others.

Reductionists about other minds (also called "behaviorists") claim, for example, that "X is in pain" means something like "X shows pain behavior." Given this definition, we can prove that X has pain by showing that X has pain behavior.

Chisholm objects that such definitions distort what it means to speak of the thoughts and feelings of others. Clearly, someone might feel pain without showing pain behavior -- or might show pain behavior without feeling pain.