There are, therefore, two aspects to knowledge; the passive sensations and the active power of synthesis. Sensations, on the one hand, are the raw material out of which reason through its various forms creates the finished fabric of knowledge. Sensations are the content of knowledge. On the other hand, there is the active unifying power of the reason. _Knowledge consists of sensations and synthesis in conjunction._ Reason alone deals with “thought relations” or imaginations, whenever it tries to treat objects of which sensations are not the raw material. Sensations alone, however, are only subjective states. The oft-quoted sayings of Kant, that “Only in experience is the truth,” and that “Conception without perception is empty, perception without conception is blind,” refer to the restriction of knowledge to the sense-materials and to the synthetic function of the reason. =The Place of Synthesis in Knowledge.= What position does synthesis occupy in the total process of knowledge? Is synthesis one of the factors or elements of knowledge? Is synthesis on the same level with the sensations, the feelings, the imaginations? No, it is very different. The synthesis that Kant is describing is not the product or conclusion from an inference. Kant does not mean by synthesis the combination of facts as a result, such as a biologist might make in framing the law of the habits of animals from his observation of them. The synthesis that Kant is talking about is not so much the result of combining experiences _as the act of combining them_. The frame of the unified manifold, the law of its unification, the act of binding the isolated experiences together is synthesis. Synthesis occupies a higher level than the elements of knowledge or knowledge itself. Synthesis is the knowing process rather than the known product. It is constitutive; it is creative; it conditions experience and puts the material of experience together. It must not be thought to be a voluntary act of the mind, which the mind will or will not do, as it pleases. When the mind acts, it synthesizes.