round, and the sum of the angles of every triangle is equal to two right angles? These illustrations are commonplace enough, indeed, but it seems to me that they clearly show the mere formality of the distinction between innate and experienced knowledge. You will recognize that both of these kinds of knowledge are different and yet of the same kind, that both are mixtures of the internal and external. Knowledge _a priori_ ceases to be a miracle when we understand that it comes out of the same fountain of experience as _a posteriori_ knowledge, and in either case knowledge is acquired only by means of the intellect. Hence intellect connected with the world is the sole source of all wisdom, and external nature as well as our internal faculty of understanding are parts of the one general nature, which is the truth and the absolute. "Only a gradual, slow, gapless development," says Noire, "can free the thinking mind from the philosophical disease of wondering." The art of dialectics or logic which teaches that the universe, or the whole world, is one being, is the science of absolute evolution. "In the whole constitution of all natural things," writes Lazare Geiger, "there is hardly anything more miraculous than the way in which the miracle avoids our glance and continuously withdraws into the distance to escape observation. In the place of the abrupt and strange things produced by imagination, reason puts uniformity and transition." And we add that the science of reason, or logic, teaches simultaneously with the unity of the whole world, also that all things are alike miraculous, or that there is only one miracle, which is existence in general, the absolute. In other words, everything and nothing is miraculous. In demonstrating that the most different things, such as heat and cold, and all radical distinctions, are only relative forms of universal nature, I prove the uninterrupted and matter of fact transition and the absolute graduality, the fusion, of all things. I have tried to establish this proof in regard to the two kinds of knowledge and illustrated it with commonplace examples, because these have a popularizing effect. In order to meet the demands of more exacting minds, I shall presently take up the miracle of causality. The indubitable statement that everything must have its cause is regarded as the most miraculous innate knowledge, and is much misused for the purpose of bringing confusion into logic. FIFTEENTH LETTER My Son: