Whatever we know of our body, we know only through sensation; i. e., by the same means by which we know of other things. Our body is to us, and is represented with the assistance of the senses, as an object in the objective world. As such it is localised and all its relations and activities are determined. Whatever subjective feeling we have concerning any state of ourselves, remains indistinct until with the help of the senses it is made an object to our observation. Who has not as yet made the experience that he was unable to localise a toothache. The pain itself gives no information either as to its nature and cause or as to the seat of the suffering. The pain itself is purely subjective. All the objective facts have to be localised with the assistance of the senses. The suspected regions must be made the object of experiments and if any irritation of a certain spot increases the ache, it will be assumed to be the seat of the pain. And even then how often is a patient mistaken not only almost always as to the nature but often also as to the seat of the pain. These facts appear strange, but they cease to be strange, when we consider that the nature of subjectivity is feeling. Subjectivity can as little become directly conscious of its own objectivity as an eye can look at itself. However, an eye can look at its image in the mirror. So the complex of subjective existence, which is through the interaction of an organism united in what we call a soul, can and does turn the channels of its own senses back upon itself and thus forms an opinion concerning its own objectivity. Man’s knowledge of his own objective existence is not due to any internal and direct perception of self, but solely to the same experience through which he receives information concerning the rest of the world. P. C. A REPLY TO A CRITIC. WITH A DISCUSSION OF NECESSARY TRUTHS. _To the Editor of The Monist_: I hope it is not a breach of etiquette to ask you to forward to your reviewer the following remarks in reply to his criticism of my work (_The Foundations of Geometry_, reviewed in Vol. II, No. 1, of _The Monist_). If he is good enough to review my second book also, I think they will clear up some misunderstandings.