These are the questions to be cleared up. Mr Bergson speaks of them chiefly in connection with the realities of consciousness, or, more generally speaking, of life. And it is here, in fact, that the consequences are most weighty and far-reaching. We shall need to refer to them again in detail. But to simplify my explanation, I will here choose another example: that of inert matter, of the perception on which the physical is based. It is in this case that the divergence between common perception and pure perception, however real it may be, assumes least proportions. Therefore it appears most in place in the sketch I desire to trace of an exceedingly complex work, where I can only hope, evidently, to indicate the main lines and general direction. We readily believe that when we cast our eyes upon surrounding objects, we enter into them unresistingly and apprehend them all at once in their intrinsic nature. Perception would thus be nothing but simple passive registration. But nothing could be more untrue, if we are speaking of the perception which we employ without profound criticism in the course of our daily life. What we here take to be pure fact is, on the contrary, the last term in a highly complicated series of mental operations. And this term contains as much of us as of things. In fact, all concrete perception comes up for analysis as an indissoluble mixture of construction and fact, in which the fact is only revealed through the construction, and takes on its complexion. We all know by experience how incapable the uneducated person is of explaining the simple appearance of the least fact, without embodying a crowd of false interpretations. We know to a less extent, but it is also true, that the most enlightened and adroit person proceeds in just the same manner: his interpretation is better, but it is still interpretation. That is why accurate observation is so difficult; we see or we do not see, we notice such and such an aspect, we read this or that, according to our state of consciousness at the time, according to the direction of the investigation on which we are engaged. Who was it defined art as nature seen through a mind? Perception, too, is an art. This art has its processes, its conventions, and its tools. Go into a laboratory and study one of those complex instruments which make our senses finer or more powerful; each of them is literally a sheaf of materialised theories, and by means of it all acquired science is brought to bear on each new observation of the student. In exactly the same way our organs of sense are actual instruments constructed by the unconscious work of the mind in the course of biological evolution; they too sum up and give concrete form and expression to a system of enlightening theories. But that is not all. The most elementary psychology shows us the amount of thought, in the correct sense of the term, recollection, or inference, which enters into what we should be tempted to call pure perception.