Everything that exists, exists due to memory. Since it lasts, it continues to endure in the same form. This is an aspect that is less taken into account by science and the scientific mentality that nowadays rules us to a certain extent.
Why can a certain thing keep its form over time and not cease to exist as soon as it appears? Answering that there is something like an inner attracting force between its components is not satisfactory because it only shifts the question to another level.
Instead of asking why a concrete thing endures in its shape, we now have to ask why the force that keeps its components together does not cease to attract them and continues acting in the same way as it did a moment or some while ago. As Hume put it, why does the Sun rise every morning and not stop its revolving motion in the celestial vault?
These are questions that science cannot answer, and does not try to. Science takes the fundamental properties of the world as they are, and it builds its knowledge upon them. When Newton established the second law of motion, the so-called principle of inertia, or when Einstein established the constant of the speed of light, they did not ask about why such properties work eternally, but they built their universes starting from these principles.
Every scientific principle shows us that the human mind tends to establish unchangeable images concerning reality. However, concrete things are not unchangeable: on the contrary, the universe, as we know it, is a tremendous space of unrest. This changeable character of things is assumed to result from the interaction of those unchangeable principles.
For example, the Newtonian principle of inertia says that a thing that another one hits, if placed in a space where no other force will act on it, will start moving in a direction in which it will continue forever at the same speed and in the same direction. However, if, during that motion, something interferes with it, that motion will be changed again.
Now, this second image of the interfering entity expresses another principle already present when we spoke about the initial motion under the first impact, which is the action of causality.
Causality is another, much more fundamental, principle than that of inertia. This principle, too, is thought of as acting as long as the universe exists. Again, science cannot question it but takes it for granted and works with it continuously.
Another principle that we need to acknowledge when dealing with knowledge is the principle of identity. It says that a thing continues to be what it is as long as nothing acts on it. It is another form of the principle of inertia, or rather one could say that the principle of inertia is its spatial and mechanical expression.
The ancient philosophers had already discovered such principles. Plato called them pure Forms or Ideas and considered them to be eternal. Aristotle spoke in this respect about secondary substances or, if we want to speak more intuitively about them, we could call them second-order beings, whereas the first-order of beings was that of concrete things.
These philosophers thought that if something is what it is, this happens because it incorporates one of those pure Forms that never changes. However, when the concrete thing changes, it happens because the initial eternal Form starts being affected in its material reflexion by the presence of another pure Form. Of course, the pure Forms do not act upon each other.
We can illustrate this with the above example of the body changing its motion under an interfering factor’s influence. The principle of inertia and the principle of causality do not interfere with each other. They are somehow completely beyond that situation. What happens here is that the body acts according to those principles as if only advised by them. The principles stay independent of that situation, and the concrete body follows their indication.
Inevitably we are forced to acknowledge here the presence of a gap between those principles and the concrete things. And because it is very difficult to grasp the nature of such a principle as something existing really out there in the world, those principles have been attributed to human reason. They have been considered more recently only as basic models that the human mind creates for itself to be able to map reality efficiently.
When Kant separated the world into two realms, the realm of the thing in itself and the realm of phenomena, he stated that principles are our projections onto the things in themselves. These projections transform them into phenomena.
However, he needed a mediator between these two worlds, a mediator that was nothing less than a conceptual Deus ex machina. He called it the productive imagination.
This productive imagination had, among other functions, the role of maintaining things in their shapes or, temporally speaking, to continue to put the sensations we get from the things in themselves into the same subjective forms.
The house that we see in front of us is the result of this productive imagination, which, while receiving sensations from outside of the human mind, puts them into the spatial form of a house and then maintains in the subjective memory the structure of this form in order to continue to pour further sensations into the same spatial form of a house.
For Kant, the productive imagination was a blind faculty of the human soul. He called it blind because it acted beyond the understanding of human reason, as, in fact, nature did; reason only received its results and operated conceptually with them.
The productive imagination had two functions: to build the present and to keep the past attached to the present, so that continuity between the past and the present could exist. However, how was it possible for this imagination to create such a continuity that was incomprehensible to human reason?
The example of the Kantian productive imagination shows us the limits of our understanding. We are faced with a universe that continues to exist in forms previously established, and this continuity determines everything in it, including psychological contents.