[31] (1) But as men at first made use of the instruments supplied by nature to accomplish very easy pieces of workmanship, laboriously and imperfectly, and then, when these were finished, wrought other things more difficult with less labour and greater perfection; and so gradually mounted from the simplest operations to the making of tools, and from the making of tools to the making of more complex tools, and fresh feats of workmanship, till they arrived at making, complicated mechanisms which they now possess. (31:2) So, in like manner, the intellect, by its native strength, [k], makes for itself intellectual instruments, whereby it acquires strength for performing other intellectual operations, [l], and from these operations again fresh instruments, or the power of pushing its investigations further, and thus gradually proceeds till it reaches the summit of wisdom. [32] (1) That this is the path pursued by the understanding may be readily seen, when we understand the nature of the method for finding out the truth, and of the natural instruments so necessary complex instruments, and for the progress of investigation. I thus proceed with my demonstration. [33] (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.