Ernst Mach asserted the the world consists entirely of sensations. Does this make him a solipsist, and how might one refute him?
Mach was a 'neutral monist', which means that he held that the fundamental units of reality are neither mental nor physical, but when they are combined in some ways they form minds and when they combined in other ways they form physical objects. He was not a solipsist, since his position allows for the existence of many minds, and perhaps even for the knowledge of their existence. By the way, even if you can't refute solipsists, it is some consolation that you can be certain that if they exist they are mistaken.