In all the sciences except Psychology we deal with objects and their changes, and leave out of account as far as possible the mind which observes them.
It should now be clear why the method of Philosophy is so different from that of the natural sciences. Experiments are not made, because they would be utterly useless.
In Psychology we deal with minds and their processes, and leave out of account as far as possible the objects that we get to know by means of them.
Common sense says that chairs and tables exist independently of whether anyone happens to perceive them or not.
The pure natural scientist is liable to forget that minds exist, and that if it were not for them he could neither know nor act on physical objects.
Our analysis of truth and falsehood, or of the nature of judgment, is not very likely to be influenced by our hopes and fears.