The problem, “Are there things in themselves?” is closely connected with the subject of my discussion with Professor Mach. Professor Mach as well as myself are aspiring to arrive at a consistent and harmonious or unitary world-conception. Both of us recognise that things in themselves have no room in a monistic philosophy, both of us recognise that concepts are means only of orientation, they are the mental tools of living beings developed as an assistance in dealing with the surrounding world. They are symbols in which the processes of nature are copied and imitated and which can serve for planning or modeling and thus predetermining the course of nature. So far we agree, but then there appears a difference which it is difficult for me to understand or formulate in precise terms. Professor Mach objects to the dualism of motion and feeling, which he declares he conceives as a unity not as a duality. But so do I. It appears to me that we must differ somehow in the method of constructing the unity. I see indeed a contrast of physical and of psychical. This contrast, however, in my conception does not belong to the object but to the subject. It is a contrast of our conception of things, but it is not a contrast existing objectively in the real things themselves. The world is not composed of the psychical and the physical, but certain features of the world are called physical, and others psychical. Both terms are abstracts. Professor Mach said in his first article and repeats it again in the present article that his former standpoint resembles very closely my present standpoint. When reading Professor Mach’s lectures of 1863, I took pains to look for the similarity, and finding many things in which I could agree I dropped the differences taking the agreements as the essential points. In reading, however, Professor Mach’s résumé of his former position as stated in this present article, I find that he attaches prominence to several points which I cannot endorse. I do not accept the theory that atoms feel, that they are endowed with consciousness. I have never spoken of atoms when dealing with psychological problems. The term “atom” is a chemical term invented as a help for thinking the equivalence of the weight of the elements which always combine in definite proportions. The term “atom” has in my opinion no sense if applied to other phenomena. The term “atom” has not been abstracted from psychical phenomena nor has it been invented for describing them. There is accordingly no probability that it can find there any appropriate application. We might as well expect that mathematical terms such as lines, points, circles, etc., are applicable in psychology. The idea of conscious circles or points can not in my mind be more absurd than that of conscious atoms. The rule must be observed that we can use abstractions made for a special purpose for that purpose only; they will not serve any other purpose as well. It is true that they