Every time we attend to somewhat, there is an idea which directs our mind, from the set of possible ideas that have some relevance to the specific situation we experience, which is the 'guiding idea', common to them all. It shares elements with all of them, relates to them, organizes them. It is the idea that prevails in the effort we make to adjust our mind to reality, when our consciousness works to give a fitting response to perceived reality. The diversity and richness of possible thoughts concretes every moment, in this way, in a single thought. Mental effort and intelligence consist precisely in that: the action of selecting the best idea of all possible. It is a more or less intense effort but in any case it is always an activity of intellectual discernment, since 'all possible ideas' can be many and they keep some relationship (more remote or less) all with the situation, 'are analogous each other or are coordinated with each other', says Bergson, thus the task of differentiation can be complex. They are intellectual elements in process of organization which are realized every moment by mental effort and reasoning.
All mental effort is actually a tendency to 'monoideism', focuses the mind and makes rely on a single representation. But from the fact that a representation is single not follows that it is a simple representation. Rather, it can be very complex, and in fact, it is precisely because of the complexity of the ideas that mental or intellectual effort occurs. The complexity determines the difficulty. Every idea that is manifested in consciousness is the result of a more or less complex process of elements discernment that grow up and interfere, related to the situation we are experiencing. There are easier and more laborious situations and representations, that require lower or higher intellectual tension; in the first case are composed of few or distinct elements, in the second case are composed of many elements or poorly differentiated. And is intelligence and experience (the wealth of knowledge, the memory) of each of us that determines the degree of definition or differentiation of elements for each of us, that is, our ability to discriminate them actually. The more we know them, the task will require less effort and stress, and the less we know them, the task will be more difficult and will generate more mental stress.
Mind, brain and external objects are an indivisible block. One define one another. Mental representations (perceptions, thoughts) occur when objects and brain are one in the presence of each other. The brain does not create reality, but is activated by external stimuli and produces certain patterns of activity in front of them, which at the manner of science we can say they represent these stimuli or situations, but in any case they constitute our phenomenal reality. Brain activity never replaces reality; they must be both simultaneously, one in the presence of the other. Brain does not create the world, simply reacts to it in a concrete way. Our memory and our knowledge does not contain the world but only a very partial representation of it, which is activated in front of it.
The brain, our whole body and the world around us are in continuous variation. We perceive in ourselves and in the world discrete states because our attention individually distincts elements of the continuum througth its 'monoideism'; the continuum of reality is beyond our mental capacities, our efforts, our intelligence, and must be converted into discrete.
Our states are not static, because if so they would not exist: there would be no change to detect, there would be nothing to detect. "If a state of the soul ceases to vary, its duration would cease to pass" says Bergson. What happens is that “it is easy not to pay attention to continuous change, and notice only when it grows large enough to print to the body a new attitude, and to attention a new direction. Just then we find that we have changed our state. Really we are constantly changing, and our states theselves are already change. (...) And because we close our eyes to the unceasing variation of every psychological state, we are obliged, when the change has become so significant that requires our attention, talking as if a new state had been juxtaposed to precedent. The new one, in turn, we assume is invariable, and so consecutively and indefinitely”.
Our attention is fixed on what is relevant, what more interests, in what best represents the situation, ie, in the 'guiding ideas', in what stands out on continuous background of our existence. Each of these states we perceive and ideas we have, "is just the better lit point of an unstable area that includes everything we feel, think, want, everything we ultimately are at a given moment".
Psychological time, phenomenal durations of things, are concepts, ideas, percepts; there is no moment, no time, without mental content: there is no psychology of nothing. The metric time of clocks is empty, it is a nothing. Empty time does not exist for us. The moments are our states, are what we perceive or think. We do not perceive the continuum of moments of the present but discrete moments that correspond always to a state, to a feeling, to an idea. We detect, we sense, we think the difference, the remarkable, not continuity. In this sense "the idea is a thought stopping; it borns when thought, instead of continuing his way, pauses or goes back on itself: the same that the heat arises in the bullet when encounters an obstacle. But as the heat did not exist before in the bullet, not the idea was an integral part of the thinking". Thought is the hidden continuous, while the idea is what appears discrete when thought, by some form of 'obstacle', what makes a 'stop'.
The whole world does not exist in our memory, in our past. Not even close. The world is always present, flowing consciousness. The past is just a useful trace to the present. "The memory of a sensation is something able to suggest that sensation, I mean, to make it reborn, stronger gradually as more attention is fixed on it. But it is different from the state it suggests, and precisely because we feel it behind the suggested sensation, we locate in the past the origin of what we experience. Indeed, the sensation is essentially present; but the memory that suggests it is presented with that power of suggestion that is the mark of what is not, of what would still be. (...) The memory appears at any time doubling perception, it borns with it, developing at same time and outlasting it because of its different nature".
The memory is a mark that has remained somewhere in the brain of a present that is past yet, and that the current present (consciousness) has reignited. The memories provide continuous information and collaborate with the sensations in generating 'guiding ideas'. They are information that the brain uses with other information as they are connected in the permanently lit consciousness circuit. This circuit does not stop to vary and evolve assimilating new energy inputs from the senses or any other external and internal environment, physically, chemically, biologically, in a dynamic equilibrium. "Willingly we represent the attentive perception as a series of processes that would walk along a single thread, the object exciting sensations, the sensations giving rise to ideas, each idea gradually shocking furthermost points of the intellectual mass. It would be, therefore, a straight running, by which the spirit would move more and more away from the object, to never return. We intend, however, that perception is a circuit in which all elements, including the same perceived object, are kept in a state of mutual tension as in an electrical circuit, such that each jerk from the object can't stop enrouting to the depths of the spirit: always it must return to the object itself". The brain is a permanently lit circuit that needs the objects and energies of the world to work.
"(...) The spirit embraces the past, while the body is confined to a present that constantly begins again. But we only think of the past because our body retains its mark still present. The impressions made by objects in the brain remain there, as images on a sensitized plate or phonograms on phonograph records; the same way that the disc repeats the melody when you power the device, also raises the brain's memory when needed jerk occurs at the point on which the printing is deposited."
In Sartre's words: "It seems that being is present, everything is present: the body, the present perception and the past as present trace in the body, everything is 'in act': as the memory-trace has not a virtual existence as memory: it is fully current trace. If the memory resurfaces, it does so in the present, as a result of a present process".
Henri Bergson, Memoria y vida.Henri Bergson, El alma y el cuerpo.
Sartre, El ser y la nada.