A differently constituted being would have a differently constituted knowledge. Our own knowledge suffices to answer the questions which result from our own mental constitution. Metaphysical Realism must ask, What is it that gives us our percepts? What is it that stimulates the subject? Monism holds that percepts are determined by the subject. But in thought the subject has, at the same time, the instrument for transcending this determination of which it is itself the author. The Metaphysical Realist is faced by a further difficulty when he seeks to explain the similarity of the world-views of different human individuals. He has to ask himself, How is it that my theory of the world, built up out of subjectively determined percepts and out of concepts, turns out to be the same as that which another individual is also building up out of these same two subjective factors? How, in any case, is it possible for me to argue from my own subjective view of the world to that of another human being? The Metaphysical Realist thinks he can infer the similarity of the subjective world-views of different human beings from their ability to get on with one another in practical life. From this similarity of world-views he infers further the likeness to one another of individual minds, meaning by "individual mind" the "I-in-itself" underlying each subject. We have here an inference from a number of effects to the character of the underlying causes. We believe that after we have observed a sufficiently large number of instances, we know the connection sufficiently to know how the inferred causes will act in other instances. Such an inference is called an inductive inference. We shall be obliged to modify its results, if further observation yields some unexpected fact, because the character of our conclusion is, after all, determined only by the particular details of our actual observations. The Metaphysical Realist asserts that this knowledge of causes, though restricted by these conditions, is quite sufficient for practical life.