Although there is but one road to science, that to wit, in which we 수원오피 proceed from things more known to things less known, from matters more manifest to matters more obscure; and universals are principally known to us, science springing by reasonings from universals to particulars; still the comprehension of universals by the understanding is based upon the perception of individual things by the senses. Both of Aristotle’s propositions, therefore, are true: First, the one in his Physics,[122] where he says, “The way is naturally prepared, from those things that are more obvious and clear to us, to those things that are more obvious and clear by nature. For, indeed, the same things are not both known to us and extant simply: whence it is indispensable to proceed in this way, viz. from those things that are of a more obscure nature, but to us are more apparent, to those that are of a nature more obvious and distinct. Now those things are, in the first instance, more perspicuous and manifest to us that are most confused in fact; whence it is necessary to proceed from universals to particulars; for the whole, according to the dictates of sense, is the more obvious; and the universal is a certain whole.” And again, that other in his Analytics,[123] where he thus expresses himself: “Singulars are to us more known, and are the first that exist according to the information of sense; for, indeed, there is nothing in the understanding which was not first in the sense. And although that reasoning is naturally prior and more known which proceeds by syllogism, still is that more perspicuous to us which is based on induction. And therefore do we more readily define singulars than universals, for there is more of{155} equivocation in universals: whence it is advisable from singulars to pass to universals.”

All this agrees with what we have previously said, although at first blush it may seem contradictory; inasmuch as universals are first imbibed from particulars by the senses, and in so far are only known to us as an universal is a certain whole and indistinct thing, and a whole is known to us according to sense. For though in all knowledge we begin from sense, because, as the philosopher quoted has it, sensible particulars are better known to sense, still the sensation itself is an universal thing. For, if you observe rightly, although in the external sense the object perceived is singular, as, for example, the colour which we call yellow in the eye, still when this impression comes to be made an abstraction, and to be judged of and understood by the internal sensorium, it is an universal. Whence it happens that several persons abstract several species, and conceive different notions, from viewing the same object at the same time. This is conspicuous among poets and painters, who, although they contemplate one and the same object in the same place at the same moment, and with all other circumstances agreeing, nevertheless regard and describe it variously, and as each has conceived or formed an idea of it in his imagination. In the same way, the painter having a certain portrait to delineate, if he draw the outline a thousand times, he will still give a different face, and each not only differing from the other, but from the original countenance; with such slight variety, however, that looking at them singly, you shall conceive you have still the same portrait set before you, although, when set side by side, you perceive how different they are. Now the reason is this: that in vision, or the act of seeing itself, each particular is clear and distinct; but the moment the object is removed, as it is by merely shutting the eyes, when it becomes an abstraction in the fancy, or is only retained in the memory, it appears obscure and indistinct; neither is it any longer appre{156}hended as a particular, but as a something that is common and universal. Seneca[124] explains this subtlety, according to Plato’s views, in very elegant terms: “An idea,” he says, “is an eternal copy of the things that have place in nature. I add an explanation of this definition, that the matter may be made plainer to you. I desire to take your portrait; I have you as the prototype of the picture, from which my mind takes a certain impression which it transfers to the canvass. The countenance, therefore, which teaches and directs me, and from which the imitation is sought, is the idea.” A little farther on he proceeds: “I have but just made use of the image which a painter forms in his mind, by way of illustration. Now, if he would paint a likeness of Virgil, he forms an intuitive image of his subject: the idea is the face of Virgil, the type of his future work; and this which the artist conveys and transfers to his work is the resemblance or portrait. What difference is there? you ask: the one is the pattern or prototype, the other the form taken from the pattern and fixed in the work; the artist imitates the one, he creates the other. A statue has a certain expression of face; this is the Eidos, the species or representation; the prototype himself has a certain expression, which the statuary conceiving, transfers to his statue: this is the idea. Do you desire yet another illustration of the distinction? The Eidos is in the work; the idea without the work, and not only without the work, but it even existed before the work was begun.” For the things that have formerly been noted, and that by use or wont have become firmly fixed in the mind of the artist, do, in fact, constitute art and the artistic faculty; art, indeed, is the reason of the work in the mind of the artist. On the same terms, therefore, as art is attained to, is all knowledge and science acquired; for as art is a habit with reference to things to be done, so is science a habit in respect of things{157} to be known: as that proceeds from the imitation of types or forms, so this proceeds from the knowledge of natural things. Each has its origin in sense and experience, and it is impossible that there can rightly be either art or science without visible instance or example. In both, that which we perceive in sensible objects differs from the image itself which we retain in our imagination or memory. That is the type, idea, forma informans; this is the imitation, the Eidos, the abstract species. That is a thing natural, a real entity; this a representation or similitude, and a thing of the reason. That is occupied with the individual thing, and itself is single and particular; this is a certain universal and common thing. That in the artist and man of science is a sensible thing, clearer, more perfect; this a matter of reason and more obscure: for things perceived by sense are more assured and manifest than matters inferred by reason, inasmuch as the latter proceed from and are illustrated by the former. Finally, sensible things are of themselves and antecedent; things of intellect, however, are consequent, and arise from the former, and, indeed, we can in no way attain to them without the help of the others. And hence it is, that without the due admonition of the senses, without frequent observation and reiterated experiment, our mind goes astray after phantoms and appearances. Diligent observation is therefore requisite in every science, and the senses are frequently to be appealed to. We are, I say, to strive after personal experience, not to rely on the experience of others; without which, indeed, no one can properly become a student of any branch of natural science, nor show himself a competent judge of what I am about to say on the subject of generation; for without experience and skill in anatomy, he would not better understand me than could one born blind appreciate the nature and difference of colours, or one deaf from birth judge of sounds. I would, therefore, have you, gentle reader, to take nothing on trust from me concerning the generation of animals; I appeal{158} to your own eyes as my witnesses and judge. For as all true science rests upon those principles which have their origin in the operation of the senses, particular care is to be taken that by repeated dissection the grounds of our present subject be fully established. If we do otherwise, we shall but come to empty and unstable opinions; solid and true science will escape us altogether: just as commonly happens to those who form their notions of distant countries and cities, or who pretend to get a knowledge of the parts of the human body, from drawings and engravings, which but too frequently present things under false and erroneous points of view. And so it is, that in the present age we have an abundance of writers and pretenders to knowledge, but very few who are really learned and philosophers.

Thus much have I thought good, gentle reader, to present to you, by way of preface, that understanding the nature of the assistance to which I have trusted, and the counsel by which I have been led in publishing these my observations and experiments; and that you yourself in passing over the same ground, may not merely be in a condition to judge between Aristotle and Galen, but, quitting subtleties and fanciful conjectures, embracing nature with your own eyes, that you may discover many things unknown to others, and of great importance.