We are perfectly justified in maintaining that only what is within ourselves can be immediately and directly perceived, and that only my own existence can be the object of a mere perception. Thus the existence of a real object outside me can never be given immediately and directly in perception, but can only be added in thought to the perception, which is a modification of the internal sense, and thus inferred as its external cause … . In the true sense of the word, therefore, I can never perceive external things, but I can only infer their existence from my own internal perception, regarding the perception as an effect of something external that must be the proximate cause … . It must not be supposed, therefore, that an idealist is someone who denies the existence of external objects of the senses; all he does is to deny that they are known by immediate and direct perception … .