To _accept_ as a spiritual fact the judgment of human nature, which assures me that when I am seeing or touching I am ‘face to face’ with a reality that exists independently of my changing sensations or ideas, instead of trying in vain by reasoning to _prove_ the existence of this reality by means of intervening sensations and ideas,—this was the alternative he adopted. I dismiss the unwarranted supposition that only my own mind and its invisible contents can be immediately manifested to me; and I fall back on the perception I have of something solid and extended, and therefore more and other than a mere sensation or idea, as what is present to me when I see and touch. Recognition of the fact that our five senses somehow bring us into a consciousness of what is neither a transitory sensation nor an idea of a sensation, but something independent of me, and that would continue to exist after I individually had ceased to exist—this recognition of external realities is Reid’s key to sound philosophy. It is a displacement of the so-called ‘ideas’ of the philosophers, and of fallacious inferences founded upon them, and a substitution of the common reasonable sense, or common judgment of reason, which neither requires nor admits of logical proof. Reid might say that what is most worth proving cannot be logically proved. We all have a direct perception of external reality which cannot be eradicated by reasoning. Abolition of the prejudice which interposed _reasonings founded on unreal ideas_ between our perception and the solid and extended reality, seemed to Reid, in virtue of its far-reaching consequences, to be the chief good he had as a philosopher secured to mankind. In his old age he writes thus to Dr. Gregory:— ‘The merit of what you are pleased to call _my philosophy_ lies, I think, chiefly in having called in question the common theory of ideas, or images of things in the mind, being the only objects of thought—a theory founded on natural prejudices, and so universally received as to be interwoven with the structure of language. Yet, were I to give you a detail of what led me to call in question this theory, after I had long held it as self-evident and unquestionable, you would think, as I do, that there was much of chance in the matter. The discovery was the birth of time, not of genius; and Berkeley and Hume did more to bring it to light than the man that hit upon it. I think there is hardly anything that can be called _mine_ in the philosophy of mind which does not follow with ease from the detection of this prejudice.’