Common-sense and natural science certainly tend to identify the objectively real with the existent in space and time. The physical universe is held to be palpably real in a way in which nothing not presented in sensuous terms can be. To most minds doubtless it is difficult to understand why Plato should have ascribed to the Ideas a higher degree of reality than that possessed by the particular objects of sense-perception, and still more difficult to understand his ascription of real existence to such Ideas as those of Beauty, Justice, and the Good. There is a certain apparent stability in a universe presented in "immediate" sense-perception--a universe with which we are in constant bodily intercourse--that seems not to belong to a mere order of relations which, if known in any sense, is not known to us through the senses. Moreover, knowledge of the physical world is felt to possess a higher degree of certainty than does any knowledge we can have of supposed economic or moral truth, or of economic or moral standards. Of such knowledge one is disposed to say, as Mr. Spencer does of metaphysics, that at the best it presupposes a long and elaborate inferential process which, as long, is likely to be faulty; whereas physical truth is immediate or else, when inference is involved in it, easy to be tested by appeal to immediate facts. Physical reality is a reality that can be seen and handled and felt as offering resistance, and this is evidence of objectivity of a sort not to be found in other spheres of knowledge for which the like claim is made.