Tetrabiblos (The Quadripartite Book)

The science of the judgments of astronomy is not completed by itself, because it cannot be completed without the science of the quadrivial astrology and the natures in which the operation is made. For if a man does not know one of the two things, whoever it may be, he will not be able to operate well in this science. ¶ But that he said "in the way of philosophy," it can be understood that he wishes to speak according to the science of natures; it can also be understood in the whole in which this science speaks, that there is an argument in the manner in which he speaks that is coming into philosophy for the sake of certifying it.

It is necessary, however, for him who is the investigator of this intention to perform, that he proceed in it by a straight path and a truthful way. Yet, in arriving at this science, in the way in which he arrives at another, which is always of one and the same mode, he should not wish to assimilate [them]. For he will postpone and deny this science if he assimilates [it].

And it arrives to one wishing to intend in this, that he should intend the way of the man seeking the truth. For this ought to be his proposal: that he not wish to seek the way of this science of the second way, [which is] of his first science, which is stable and firm and of one mode. For if a man were to do this, he would have to immediately reprove and render this science mendacious.

He wishes to say: he who seeks the prognostications of this science to know [them] as certainly as those of the quadrivial science, errs. Because the prognostications of the quadrivial astrology, just as it is to know when eclipses and conjunctions will be which follow the courses of the planets, never change. The prognostications, however, of this science are of another mode, because the matters in which the superior bodies operate are changed easily, and because they are not firm nor do they remain of one mode.

For the short duration of the accidents of the matter in which these things are turned, this science is the occasion of the second mutation. ¶ This nature, because matter never persists in the same state, is why he who touched the perfection of this science [did so] with difficulty.

The reason for which this science is changed is because the element in which the operation is made of this science is not stable, nor does it remain in one mode, and on account of this it is difficult to understand the apparatus which is in it.

After he assigned to us the reason which is certain concerning the quadrivial astrology, he gave us the reason in this saying: why the science of the judgments of astronomy is of another manner than the first. It is true that of all science they have one difference, yet the error which falls into this [science] of judgments is on account of the element in which the operation is made of this science. He wishes to say by the four elements which are composed of them, such as fumes, minerals, vegetables, and animals. For these things receive operations by many manners, and none of them is stable in one state. And on account of this, it is difficult to know the things happening in them. From these, therefore, it can be understood that the error falling in this science is not because of the science, but because of the accidents of the matter in which they operate of it.

On this, however, it is not to be postponed by any cause of sloth, since it is striven to know what can be known from it. It is plain indeed that, for those which we have, it is the occasion of many accidents and mutations happening in this world.

It does not, however, happen for all that because this happens, that we should leave off looking into things which can be known of this science. Because it is manifest that for the greater part, the accidents and novelties which have happened among us do not come on account of any other thing except on account of that which holds us surrounded.

After Ptolemy made [us] understand that the error which falls in this science is not except on account of the matter which is not stable, he says to us that we should not deviate [from it] for this reason, when we look through this science into those things which can be known by a man of it. Because it is manifest that the mutations and works happening among us happen on account of the figures and courses of the stars. And after it is thus, the previous error ought not to deviate us from the great profit which we can have of it.

Which indeed is of many to despise the difficult things to investigate, which from the blindness of the mind and from its ignorance they were postponing the first science on account of the accidents, but some the second.

And because many men make things mendacious which are difficult to understand, there are among them those who thus come to a great blindness, that they say the first of these sciences is mendacious and others the second, vilifying the same.

The quadrivial astrology is difficult to understand because there are strong reasons from geometry and arithmetic in it, because of the rectifications of the ancients, which are of diverse opinions, because of the error which happens in the division of those with whom it was looked into, and because of the length of time which is between one rectification and another. And the science of the judgments of astronomy is difficult to understand because of the element which is not stable as we said before, and because of the difficulty of understanding the composition which is made of the virtues of the planets, namely, one with another. And on account of this, some come to such great blindness—he wishes to say, blindness of the intellect—that they say the first science is mendacious. For they vilify many things and [those that are] very good and more perfect in philosophy because it is difficult to understand them. And there are others who say the second is mendacious and vilify it for this same reason. Ptolemy, however, added in his statement these two sciences: so that you may understand that each of them is well certain in itself, [and] that the difficulty and error which happens in them is on account of the debility of the intellect of man, and on account of the nature of the element which is not stable. And after it is thus, neither of these sciences can be justly vilified.

The occasion that draws those to these things thus is perhaps this: either they are as some who, because of the excessive difficulty, cannot know [them], [and] they do not estimate at all that others can know, or perhaps just as those who, although they may be able to know, repudiate [them] because they flow away lightly from memory. By these things, therefore, for these causes, they were holding this science of no account as they vilify [it].

And the reason for which we can say that this happens to them is: because there are some who, because they cannot understand a thing, believe that it cannot be in any way, and that there is no one who can reach it. And there are some of the opinion that a man ought not to look into a thing difficult to know, and they disdain it; and on account of this, they do not look into the proposal of these sciences, and they say that it is a thing which a man cannot reach.

Ptolemy in this place, assigning the reason why many vilify the science of the judgments of astronomy, says that it is of two things. One on account of which they do this: either because they believe that there are no men who can understand in any way things which are difficult to understand, or because they see some err there. Because they cannot know the whole on account of some thing which is lacking, they disdain the whole for themselves, and they estimate that it is a thing which no one can know, just as the others whom we said. The difference, however, which is between one opinion and another is that the first ones whom we said estimate that there is no man who can understand it in any way. And the others estimate that it is a thing which can be reached, but it is so difficult that one ought not to look into it. And on account of this, they disdain the same.

We, however, before we make manifest the particulars of this science, will strive to prove briefly what in this a man can know of the science of prognostication, which fruit follows, and from these two we will begin to explain how much it is that we can attain from this science.

We will narrate so that we may make it understood briefly how much of prognostication a man can attain from this science and how much is the profit which lies in it before we speak of the things particular to these sciences. Beginning first so that we may make it understood how much is that which a man can attain from this science.

After he narrated the reason for which the error can fall in this art, saying that it is on account of the element which is not stable, and because it is difficult to know the compositions which are made on account of the commixture of the virtues of the planets, and on account of this many disdain the same, he now begins to prove that it is a true and certain science. And he wishes to show how much a man can attain of it and how much is the profit which lies in it, so that men may have a better will in it and may desire it more.

How we can arrive at the prognosticable science of the judgments of the stars, and how much is that which can be known from it.