卷一·第一章　引言

Of the means of prediction through astronomy, O Syrus, two are the most important and valid. One, which is first both in order and in effectiveness, is that whereby we apprehend the aspects of the movements of sun, moon, and stars in relation to each other and to the earth, as they occur from time to time; the second is that in which by means of the natural character of these aspects themselves we investigate the changes which they bring about in that which they surround.

叙鲁斯啊，星占预言的方法之中，最重要、最有效的有两种。第一种在次序上和效力上都居首位，凭它，我们掌握日、月与诸星的运动彼此之间、以及对大地随时形成的相位；第二种则凭这些相位本身的自然特性，考察它们在其所环绕之物中引起的变化。

The first of these, which has its own science, desirable in itself even though it does not attain the result given by its combination with the second, has been expounded to you as best we could in its own treatise by the method of demonstration.

第一种自成一门学问，即使达不到与第二种结合时所得的成果，本身也值得追求；我们已在专论它的《天文学大成》里，用证明的方法尽力向你阐述过了。

We shall now give an account of the second and less self-sufficient method in a properly physical way, so that one whose aim is the truth might never compare its perceptions with the sureness of the first, unvarying science, for he ascribes to it the weakness and unpredictability of material qualities found in individual things, nor yet refrain from such investigation as is within the bounds of possibility, when it is so evident that most events of a general nature draw their causes from the enveloping heavens.

现在我们要以合乎自然哲学的方式，叙述第二种、不那么自足的方法。这样，追求真理的人既不会把它的认识拿来与第一种恒常不变之学的确定性相比，因为他认定它带有个别事物中物质性质的那种软弱与难以预料；也不会放弃在可能范围之内的这类研究，因为大多数具有普遍性质的事件，显然都从周天取得其原因。

But since everything that is hard to attain is easily assailed by the generality of men, and in the case of the two before-mentioned disciplines the allegations against the first could be made only by the blind, while there are specious grounds for those levelled at the second — for its difficulty in parts has made them think it completely incomprehensible, or the difficulty of escaping what is known has disparaged even its object as useless — we shall try to examine briefly the measure of both the possibility and the usefulness of such prognostication before offering detailed instruction on the subject. First as to its possibility.

然而，凡是难以达到的东西，都容易遭到一般人的攻击；就前面所说的两门学问而言，对第一门的指责只有瞎子才说得出口，对第二门的指责却有些貌似有理的根据——它在某些部分的艰难，使人以为它完全不可理解；或者，已知之事难以逃避，又使人连它的目标也贬为无用——因此，在详细传授这门学问之前，我们先简要考察这种预言可能到什么程度、有用到什么程度。先说它的可能。