What kind of attention is required to preserve certainty in our knowledge

How modifications of the soul make it attentive, yet divide its capacity for perception**

From the very beginning of this work, we have shown that the understanding only perceives, and that there is no difference within the understanding itself between simple perceptions, judgments, and reasonings — except that judgments and reasonings are far more complex perceptions than simple ones. For simple perceptions present only things themselves to the mind; judgments present the relations between things; and reasonings — if they are simple — present relations between those relations. If they are more complex, they present relations of relations, or compound relations holding between the relations of things, and so on indefinitely. As relations multiply, the reasonings that represent them to the mind become more intricate. Even so, judgments, simple reasonings, and compound reasonings remain nothing but pure perceptions on the part of the understanding — for the understanding, as we have already stated at the start of Book One, does nothing but perceive.

Since judgments and reasonings are, in the understanding, nothing more than pure perceptions, it follows clearly that the understanding itself never falls into error. For error is not found in perceptions, nor is it even intelligible. Ultimately, error or falsehood is nothing but a relation that does not exist — and what does not exist can neither be seen nor understood. We can see that two times two equals four, or that two times two does not equal five; there is a real relation of equality between two times two and four, and a real relation of inequality between two times two and five. In this way, truth is intelligible. But we can never see that two times two equals five, because there is no such relation of equality there; and what does not exist cannot be perceived. As we have said many times before, error consists only in a hasty consent of the will — a will dazzled by some false glimmer, which, instead of preserving its freedom as far as it can, rests lazily upon the mere appearance of truth.

Nevertheless, because the understanding usually has only confused and imperfect perceptions of things, it becomes a causa occasionalis or indirect source of our mistakes. Just as our bodily vision often leads us into error by representing external objects only in a confused and incomplete way — confusedly when they are too distant or light is insufficient, and incompletely because it shows only the side facing us — so too the understanding often perceives things only confusedly and imperfectly. This happens when objects are not sufficiently present to it, or when it fails to grasp all their parts. As a result, the will falls into countless errors by yielding too readily to these obscure and incomplete perceptions.

We must therefore seek ways to prevent our perceptions from being confused and imperfect. And since nothing makes them clearer and more distinct than attention — as everyone acknowledges — we must find methods to help us become more attentive than we naturally are. Only in this way can we preserve certainty in our reasoning, and even grasp at a single glance the necessary connection between all parts of our longest chains of deduction.

To find these methods, we must firmly hold to what we have explained elsewhere: the mind does not give equal attention to everything it perceives. It applies itself infinitely more to what affects it, alters it, and penetrates it, than to things that are present but do not touch it or belong to it. In short, it dwells far more upon its own inner states than upon the mere ideas of external objects — ideas that are distinct from the mind itself. This is why we consider the abstract ideas of pure understanding only with reluctance and little focus; why we apply ourselves much more readily to what we can imagine, especially when our imagination is strong and leaves deep traces in the brain; and finally why we become wholly absorbed in sensible qualities, unable to turn our attention to the pure ideas of the mind whenever we feel something intensely pleasant or painful. For pleasure, pain, and other sensations are nothing but states of the mind itself — so we cannot help but be aware of them, and our mind’s capacity for perception is entirely occupied by them, since all sensations are nothing more than perceptions.

The same is not true of the mind’s pure ideas. We may have them intimately united with our mind, yet still consider them with almost no attention. For although God is most intimately united to us, and it is in Him that the ideas of all things we see reside, these ideas remain hidden from us while the movement of the animal spirits does not awaken their traces, or while our will does not direct the mind toward them — that is, while it does not produce those mental acts to which the Author of Nature has linked the representation of these ideas. These truths form the foundation for everything we shall say about the aids that can sharpen our attention. Being rooted in the very nature of the mind, such aids are not likely to be fanciful or useless, like many others that only confuse more than they help. Even if they do not achieve all we might hope, reading about them will not be a complete waste of time — for we shall come to understand our own mental nature far better.

The modifications of the soul arise from three sources: the senses, the imagination, and the passions. Everyone knows from experience that intense pleasures and pains, vivid imaginings, and strong passions so fully occupy the mind that it becomes incapable of sustained attention while these feelings are too acute — its entire capacity or faculty of perception is then filled. Even when such states are moderate, they still divide the mind’s capacity, at least to some degree, so that it cannot devote its full power to considering truths that are somewhat abstract.

From this follows an important conclusion: anyone who wishes to apply themselves seriously to the search for truth must take great care to avoid, as far as possible, all overly strong sensations — such as loud noises, harsh light, excessive pleasure or pain, and the like. They must constantly guard the purity of their imagination, preventing the formation of deep impressions in the brain that would disturb and scatter their thoughts. Most of all, they must restrain the movements of the passions, which leave such powerful marks upon both body and soul that it is usually almost impossible for the mind to think of anything other than the objects that aroused them. Even though the pure ideas of truth are always present to us, we cannot reflect upon them while our capacity for thought is filled with these penetrating inner states.

The soul cannot exist without some feeling, emotion, or other particular modification.

And so we must turn necessity into advantage and draw even from these states some help toward greater attention. Doing so, however, requires great skill and caution. We must carefully assess our need for such aids, and make use of them only insofar as the need to focus our attention truly demands it.