On the Improvement of Understanding, by Benedict de Spinoza, , at sacred-texts.com
 (1) A true idea, [m], (for we possess a true idea) is something different from its correlate (ideatum); thus a circle is different from the idea of a circle. (2) The idea of a circle is not something having a circumference and a center, as a circle has; nor is the idea of a body that body itself. (3) Now, as it is something different from its correlate, it is capable of being understood through itself; in other words, the idea, in so far as its actual essence (essentia formalis) is concerned, may be the subject of another subjective essence (essentia objectiva). [33note1] (4) And, again, this second subjective essence will, regarded in itself, be something real, capable of being understood; and so on, indefinitely.
 (1) For instance, the man Peter is something real; the true idea of Peter is the reality of Peter represented subjectively, and is in itself something real, and quite distinct from the actual Peter. (2) Now, as this true idea of Peter is in itself something real, and has its own individual existence, it will also be capable of being understood—that is, of being the subject of another idea, which will contain by representation (objective) all that the idea of Peter contains actually (formaliter). (3) And, again, this idea of the idea of Peter has its own individuality, which may become the subject of yet another idea; and so on, indefinitely. (4) This everyone may make trial of for himself, by reflecting that he knows what Peter is, and also knows that he knows, and further knows that he knows that he knows, &c. (34:5) Hence it is plain that, in order to understand the actual Peter, it is not necessary first to understand the idea of Peter, and still less the idea of the idea of Peter. (6) This is the same as saying that, in order to know, there is no need to know that we know, much less to know that we know that we know. (7) This is no more necessary than to know the nature of a circle before knowing the nature of a triangle. [n]. (8) But, with these ideas, the contrary is the case: for, in order to know that I know, I must first know.
 (1) Hence it is clear that certainty is nothing else than the subjective essence of a thing: in other words, the mode in which we perceive an actual reality is certainty. (2) Further, it is also evident that, for the certitude of truth, no further sign is necessary beyond the possession of a true idea: for, as I have shown, it is not necessary to know that we know that we know. (3) Hence, again, it is clear that no one can know the nature of the highest certainty, unless he possesses an adequate idea, or the subjective essence of a thing: certainty is identical with such subjective essence.
 (1) Thus, as the truth needs no sign—it being to possess the subjective essence of things, or, in other words, the ideas of them, in order that all doubts may be removed—it follows that the true method does not consist in seeking for the signs of truth after the acquisition of the idea, but that the true method teaches us the order in which we should seek for truth itself, [o] or the subjective essences of things, or ideas, for all these expressions are synonymous.
 (1) Again, method must necessarily be concerned with reasoning or understanding—I mean, method is not identical with reasoning in the search for causes, still less is it the comprehension of the causes of things: it is the discernment of a true idea, by distinguishing it from other perceptions, and by investigating its nature, in order that we may so train our mind that it may, by a given standard, comprehend whatsoever is intelligible, by laying down certain rules as aids, and by avoiding useless mental exertion.
 (1) Whence we may gather that method is nothing else than reflective knowledge, or the idea of an idea; and that as there can be no idea of an idea—unless an idea exists previously,—there can be no method without a pre-existent idea. (2) Therefore, that will be a good method which shows us how the mind should be directed, according to the standard of the given true idea. (38:3) Again, seeing that the ratio existing between two ideas the same as the ratio between the actual realities corresponding to those ideas, it follows that the reflective knowledge which has for its object the most perfect being is more excellent than reflective knowledge concerning other objects—in other words, that method will be most perfect which affords the standard of the given idea of the most perfect being whereby we may direct our mind.
 (1) We thus easily understand how, in proportion as it acquires new ideas, the mind simultaneously acquires fresh instruments for pursuing its inquiries further. (2) For we may gather from what has been said, that a true idea must necessarily first of all exist in us as a natural instrument; and that when this idea is apprehended by the mind, it enables us to understand the difference existing between itself and all other perceptions. (3) In this, one part of the method consists. (39:4) Now it is clear that the mind apprehends itself better in proportion as it understands a greater number of natural objects; it follows, therefore, that this portion of the method will be more perfect in proportion as the mind attains to the comprehension of a greater number of objects, and that it will be absolutely perfect when the mind gains a knowledge of the absolutely perfect being, or becomes conscious thereof.
 (1) Again, the more things the mind knows, the better does it understand its own strength and the order of nature; by increased self-knowledge, it can direct itself more easily, and lay down rules for its own guidance; and, by increased knowledge of nature, it can more easily avoid what is useless. (2) And this is the sum total of method, as we have already stated.
 (1) We may add that the idea in the world of thought is in the same case as its correlate in the world of reality. (2) If, therefore, there be anything in nature which is without connection with any other thing, and if we assign to it a subjective essence, which would in every way correspond to the objective reality, the subjective essence would have no connection, [p] with any other ideas—in other words, we could not draw any conclusions with regard to it. (41:3) On the other hand, those things which are connected with others—as all things that exist in nature—will be understood by the mind, and their subjective essences will maintain the same mutual relations as their objective realities—that is to say, we shall infer from these ideas other ideas, which will in turn be connected with others, and thus our instruments for proceeding with our investigation will increase. (4) This is what we were endeavoring to prove.
 (1) Further, from what has just been said—namely, that an idea must, in all respects, correspond to its correlate in the world of reality,—it is evident that, in order to reproduce in every respect the faithful image of nature, our mind must deduce all its ideas from the idea which represents the origin and source of the whole of nature, so that it may itself become the source of other ideas.