There are propositions of which we may say that they describe facts in the material world (external world). Roughly speaking, they treat of physical objects; bodies, fluids, etc.. I am not thinking in particular of the laws of the natural sciences, but of any such proposition as “the tulips in our garden are in full bloom”, or “Smith will come in any moment”. There are on the other hand propositions describing personal experiences, as when the subject in a psychological experiment describes his sense-experiences; say his visual experience, independent of what bodies are actually before his eyes and, N.B., independent also of any processes which might be observed to take place in his retina, his nerves, his brain, or other parts of his body. (That is, independent of both physical and physiological facts.)