Upon the question of fact in ordinary scientific inquiry little difficulty is experienced. Indeed it might on a cursory view even appear ridiculous if the demand were made that we had to prove in geometry, for instance, that there were such objects as space, and geometrical figures, or in astronomy and physics that there was a sun, stars, and magnetic phenomena. In these sciences, which are concerned with what is actually presented to sense perception, objects are accepted from objective experience, and so far from it being regarded necessary to demonstrate (_beweisen_) them, it is deemed sufficient to point to (_weisen_) the bare facts. Yet even within the limits of non-philosophical instruction doubts may arise as to the existence of certain objects. In psychology, for example, the science of mind, the doubt is possible whether there _is_ a soul, an intelligence, _i.e._, something distinct from material conditions, something immaterial[33], independent and self-substantive, or in the theology whether a God actually _exists._ Moreover, assuming the objects of the science to be thus immaterial, in other words, merely present in the mind, and not a part of the objective world we perceive, we have to face the possible conviction that there is nothing in the mind, but that which it has evoked in virtue of its own activity. This brings up incidentally the question whether men have produced this idea or intuition which is inward to their minds or not, and even if we do actually accept the first alternative, whether they have not made such an idea once more to vanish, or depreciated, the same at any rate to an idea of wholly _subjective_ validity, whose content possesses no independent or self-contained existence[34]. In this way, for example, the beautiful has been frequently regarded as possessing no necessarily essential and independent stability in the world of our ideas; rather it is accepted as a pleasure purely personal to ourselves, due to the caprice of our senses[35]. Even our external intuitions, observations and perceptions frequently deceive and lead us astray; but still more is this the case with those ideas that do not arise from sense-perception, even though they possess in themselves the greatest vitality, and are able to transport us into passion, we are powerless to resist.