Speaking in popular and unphilosophical terms, we may say that the content of a thought is supposed to be something in your head when you think the thought, while the object is usually something in the outer world. It is held that knowledge of the outer world is constituted by the relation to the object, while the fact that knowledge is different from what it knows is due to the fact that knowledge comes by way of contents. We can begin to state the difference between realism and idealism in terms of this opposition of contents and objects. Speaking quite roughly and approximately, we may say that idealism tends to suppress the object, while realism tends to suppress the content. Idealism, accordingly, says that nothing can be known except thoughts, and all the reality that we know is mental; while realism maintains that we know objects directly, in sensation certainly, and perhaps also in memory and thought. Idealism does not say that nothing can be known beyond the present thought, but it maintains that the context of vague belief, which we spoke of in connection with the thought of St. Paul's, only takes you to other thoughts, never to anything radically different from thoughts. The difficulty of this view is in regard to sensation, where it seems as if we came into direct contact with the outer world. But the Berkeleian way of meeting this difficulty is so familiar that I need not enlarge upon it now. I shall return to it in a later lecture, and will only observe, for the present, that there seem to me no valid grounds for regarding what we see and hear as not part of the physical world. Realists, on the other hand, as a rule, suppress the content, and maintain that a thought consists either of act and object alone, or of object alone. I have been in the past a realist, and I remain a realist as regards sensation, but not as regards memory or thought. I will try to explain what seem to me to be the reasons for and against various kinds of realism.