Tetrabiblos (The Quadripartite Book)

Since, therefore, these things are of this kind, it is proven in general and individual things, and those accidents whose primary occasion is stronger and greater than all occasions contrary to them will necessarily happen. It must be known, also, that those which are not thus, when they have received a contrary [force] of equal strength, will be easily changed. Those, however, which do not find this will imitate their primary natures.

And after these are as we have said before, we understand well regarding all things, both universal as well as particular, to which accidents happen, if the primary thing were stronger and greater than other contrary things, without doubt it is necessary that the greater entirely overcomes the smaller; and those which are not thus, having an equality of weakness, can be changed easily with some preparation; and if a contrary accident does not arrive, it will follow its primary nature.

He wishes to say that the works which the stars perform in terrestrial things, both universal as well as particular, are of one manner in this: that those things which have more strongly a contrary [force] must entirely be the profit, or [it means] that a man has this in knowing this prognostication, because it soothes the will so that the thing itself does not happen to him impetuously. Those, however, which have contrary [forces] equal in virtue, can be changed easily and diverted by some preparation of one of them. And if preparation were not made in this, the accident will happen which the first principle will demonstrate.

That sloth and ignorance happens through unnecessary forces.

This, however, will be by necessity and in great lack of necessity.

He wishes to say that the works of the stars which have a great contrary [force] in virtue do not pass to us except by our lack of necessity, because we will not make a preparation to divert it, because they are not necessary to happen. And in these, the knowledge of prognostication is of great profit because we shall be able to divert the evil in the manner in which it will not come. Wherefore, for example, when we have known that the star of Mars will cause someone an infirmity of choler in the head for one month, we shall be able to oppose this by purging the choler and tempering their complexions with cold and moist things; and when we have done this, we shall be able to liberate him from this sickness. Then if it happens, it will be very little in respect to that which would have been had we not done this.

The same we see happening also in all things whose beginnings are natural: as in the natures of certain stones and vegetables, and also wounds and apostemes, and infirmities, which necessarily operate something, of which some are such that they operate unless they are contradicted by something contrary.

We see this same thing happening in all others having natural beginnings, since it is from the nature of some stones and vegetables, animals, wounds, and infirmities to operate something necessarily, such that it cannot be otherwise. And some of them operate this unless the thing has contrary [forces] operating.

He says that this which he said is not only in the works of the stars, but is in the works of other natural things, because none of them has a contrary thing by its own [nature] which can disturb it. Just as with a great fire when it falls into dry herbs, or from a poison very strong, or from large and deep wounds from which a man cannot be liberated, or from a strong apparatus of a great infirmity, or from infirmities that are dangerous and very strong. For there are some of these from which a man cannot be liberated by any preparation that he makes. And there are some which have a contrary [force] by which a man can be liberated, and that accident can be disturbed. Ptolemy, however, adds—

that he might make us [understand] that both of these are natural things and can be changed; yet some of them are such that they cannot be disturbed in any way, but it is expedient that they be altogether. And of them are those which have a contrary [force] which can make them contrary.

Similarly, it is appropriate for all who are versed in this science to consider the accidents which happen to men, and to prognosticate in them naturally, and so that they do not adhere to false opinions, since some things cannot be avoided for the reason that the occasions from which they proceed are many and great, but others are the contrary alterations which they receive; just as physicians, to whom the infirmities of men become known, predict which of them are curable and which, however, are not.

For it is appropriate that they understand in this way, those who wish to know from this science what are the accidents happening to men, and that they first judge according to nature, not looking to empty opinions in their judgments, since some things are such that a man cannot guard himself in any way, and for the reason that the causes from which they come are very strong and great; and of them are those of the manner that can receive a change, just as physicians ought to understand concerning infirmities which of them are mortal, not being able to have a remedy, and which of them can have a remedy through medicine.

That which he said, that they judge first according to nature, he wishes to say that when a man will have judged, he should judge as in those things which can be changed, since natural things change, and he does not speak of a thing which in every way must be and cannot remain, except of those which come through great, many, and strong causes. For of such, it must be judged that they will happen in every way. And that which he said, of the manner of those which can receive a change, he wishes to say that there are those from which we can be liberated by some guarding, because they come from a weak cause. And in such things, we ought to say: "this will be unless a guard is applied there." That which he said, just as physicians can know concerning infirmities which are mortal and which can be liberated through medicine, he wishes to say that for an astrologer it is appropriate that he know that from the works of the stars there are necessary [things] from which no one can be liberated, and this he should judge by itself on one side; and on the other side, those from which one can be liberated, just as good physicians do when they see an infirmity which cannot be cured, they do not busy themselves with it because they do not wish to labor over a useless thing. But when they understand that it can be liberated, they apply their mind to it and cure it.

In things also in which an alteration can attend, we ought to note from the modes of the judgments that which he adds. When in the nativity of anyone the astrologer says that when his complexion shall be such, and the change of the air shall have been such, and the tempered complexion shall have been altered, there follows such an infirmity according to increase or diminution, and just as when the physician says: "this infirmity or these ulcers will increase and will putrefy." And similarly if one, knowing the natures of things, says that a magnet attracts iron, each one of these, if the slowness of the craftsman does not apply its contrary, will happen necessarily and will proceed according to the powers of its own proper nature, and the ulcers will not increase nor putrefy when medicine opposes them. Nor also will the magnet stone attract iron if it is greased with garlic.

Furthermore, in those which can be changed, it is appropriate that he judge—