Reid defended common sense against scepticism by appeal to the claim that our faculties should be considered trustworthy until some argument proves them to be untrustworthy. He believed, of course, that no such argument would be forthcoming. In this paper, we shall investigate Reid's defense of the faculty of perception and the evidence of the senses by analogy with the faculty of language and the evidence of testimony. Reid argued that the evidence of testimony should be trusted unless there is reason to think it untrustworthy and by analogy, that the evidence of the senses should be trusted unless there is reason to think it untrustworthy. He admitted the fallibility of such evidence but contended that such fallibility is characteristic of all our faculties. Moreover, and perhaps most important, Reid developed a psychological theory of the faculties of perception and language that showed the analogy between these two faculties to be very exact indeed.