CHANGE OF STATE AND CHANGE OF POSITION.--But, it will be said, if the idea of geometric space is not imposed upon our mind, and if, on the other hand, none of our sensations can furnish it, how could it have come into existence? This is what we have now to examine, and it will take some time, but I can summarize in a few words the attempt at explanation that I am about to develop. _None of our sensations, isolated, could have conducted us to the idea of space; we are led to it only in studying the laws, according to which these sensations succeed each other._ We see first that our impressions are subject to change; but among the changes we ascertain we are soon led to make a distinction. At one time we say that the objects which cause these impressions have changed state, at another time that they have changed position, that they have only been displaced. Whether an object changes its state or merely its position, this is always translated for us in the same manner: _by a modification in an aggregate of impressions_. How then could we have been led to distinguish between the two? It is easy to account for. If there has only been a change of position, we can restore the primitive aggregate of impressions by making movements which replace us opposite the mobile object in the same _relative_ situation. We thus _correct_ the modification that happened and we reestablish the initial state by an inverse modification. If it is a question of sight, for example, and if an object changes its place before our eye, we can 'follow it with the eye' and maintain its image on the same point of the retina by appropriate movements of the eyeball. These movements we are conscious of because they are voluntary and because they are accompanied by muscular sensations, but that does not mean that we represent them to ourselves in geometric space. So what characterizes change of position, what distinguishes it from change of state, is that it can always be corrected in this way. It may therefore happen that we pass from the totality of impressions _A_ to the totality _B_ in two different ways: 1º Involuntarily and without experiencing muscular sensations; this happens when it is the object which changes place; 2° Voluntarily and with muscular sensations; this happens when the object is motionless, but we move so that the object has relative motion with reference to us. If this be so, the passage from the totality _A_ to the totality _B_ is only a change of position. It follows from this that sight and touch could not have given us the notion of space without the aid of the 'muscular sense.'