This is an essay on G. E. Moore’s argument in defense of common sense against David Hume’s theory. However, the burden of essay is to show that, though Moore derived has argument from Thomas Reid, it was the latter who noted that the defense of common sense required more than showing that Hume’s theory conflicted with common sense. It required supplying a better theory than that of Hume’s of the operations of the human mind, and especially, a better theory of the evidence and justification of common sense beliefs. The essay is a formulation and defense of Reid’s theory of conception, conviction and evidence.