Book XII Chapter 6

Since there were three kinds of substance, two of them physical and one unmovable, regarding the latter we must assert that it is necessary that there should be an eternal unmovable substance. For substances are the first of existing things, and if they are all destructible, all things are destructible. But it is impossible that movement should either have come into being or cease to be (for it must always have existed), or that time should. For there could not be a before and an after if time did not exist. Movement also is continuous, then, in the sense in which time is; for time is either the same thing as movement or an attribute of movement. And there is no continuous movement except movement in place, and of this only that which is circular is continuous.

But if there is something which is capable of moving things or acting¹ on them, but is not actually doing so, there will not necessarily be movement; for that which has a potency² need not exercise it. Nothing, then, is gained even if we suppose eternal substances, as the believers in the Forms do, unless there is to be in them some principle which can cause change; nay³, even this is not enough, nor is another substance besides the Forms enough; for if it is not to act, there will be no movement. Further even if it acts, this will not be enough, if its essence is potency; for there will not be eternal movement, since that which is potentially may possibly not be. There must, then, be such a principle, whose very essence is actuality. Further, then, these substances must be without matter; for they must be eternal, if anything is eternal. Therefore they must be actuality.

Yet there is a difficulty; for it is thought that everything that acts is able to act, but that not everything that is able to act acts, so that the potency is prior. But if this is so, nothing that is need be; for it is possible for all things to be capable of existing but not yet to exist.

Yet if we follow the theologians who generate the world from night, or the natural philosophers who say that ‘all things were together’, the same impossible result ensues. For how will there be movement, if there is no actually existing cause? Wood will surely not move itself-the carpenter’s art must act on it; nor will the menstrual blood nor the earth set themselves in motion, but the seeds must act on the earth and the semen on the menstrual blood.

This is why some suppose eternal actuality-e.g. Leucippus and Plato; for they say there is always movement. But why and what this movement is they do say, nor, if the world moves in this way or that, do they tell us the cause of its doing so. Now nothing is moved at random⁴, but there must always be something present to move it; e.g. as a matter of fact a thing moves in one way by nature, and in another by force or through the influence of reason or something else. (Further, what sort of movement is primary? This makes a vast difference.) But again for Plato, at least, it is not permissible⁵ to name here that which he sometimes supposes to be the source of movement-that which moves itself; for the soul is later, and coeval⁶ with the heavens, according to his account. To suppose potency prior to actuality, then, is in a sense right, and in a sense not; and we have specified⁷ these senses. That actuality is prior is testified by Anaxagoras (for his ‘reason’ is actuality) and by Empedocles in his doctrine⁸ of love and strife⁹, and by those who say that there is always movement, e.g. Leucippus. Therefore chaos¹⁰ or night did not exist for an infinite time, but the same things have always existed (either passing through a cycle of changes or obeying some other law), since actuality is prior to potency. If, then, there is a constant cycle, something must always remain, acting in the same way. And if there is to be generation and destruction, there must be something else which is always acting in different ways. This must, then, act in one way in virtue¹¹ of itself, and in another in virtue of something else-either of a third agent, therefore, or of the first. Now it must be in virtue of the first. For otherwise this again causes the motion both of the second agent and of the third. Therefore it is better to say ‘the first’. For it was the cause of eternal uniformity; and something else is the cause of variety, and evidently both together are the cause of eternal variety. This, accordingly, is the character which the motions actually exhibit. What need then is there to seek for other principles?

1 acting   

n.演戏，行为，假装；adj.代理的，临时的，演出用的

参考例句：

• Ignore her,she's just acting.别理她，她只是假装的。
• During the seventies,her acting career was in eclipse.在七十年代，她的表演生涯黯然失色。

2 potency   

n. 效力，潜能

参考例句：

• Alcohol increases the drug's potency.酒精能增加这种毒品的效力。
• Sunscreen can lose its potency if left over winter in the bathroom cabinet.如果把防晒霜在盥洗室的壁橱里放一个冬天，就有可能失效。

3 nay   

adv.不；n.反对票，投反对票者

参考例句：

• He was grateful for and proud of his son's remarkable,nay,unique performance.他为儿子出色的，不，应该是独一无二的表演心怀感激和骄傲。
• Long essays,nay,whole books have been written on this.许多长篇大论的文章，不，应该说是整部整部的书都是关于这件事的。

4 random   

adj.随机的；任意的；n.偶然的(或随便的)行动

参考例句：

• The list is arranged in a random order.名单排列不分先后。
• On random inspection the meat was found to be bad.经抽查，发现肉变质了。

5 permissible   

adj.可允许的，许可的

参考例句：

• Is smoking permissible in the theatre?在剧院里允许吸烟吗？
• Delay is not permissible,even for a single day.不得延误，即使一日亦不可。

6 coeval   

adj.同时代的；n.同时代的人或事物

参考例句：

• Analysis has proved that this document is coeval with that one.这份文件经分析证明与那一份是同一个时代的。
• He believes that cooking and humanity are coeval.他相信烹饪和人类是同时代的。

7 specified   

adj.特定的

参考例句：

• The architect specified oak for the wood trim. 那位建筑师指定用橡木做木饰条。
• It is generated by some specified means. 这是由某些未加说明的方法产生的。

8 doctrine   

n.教义；主义；学说

参考例句：

• He was impelled to proclaim his doctrine.他不得不宣扬他的教义。
• The council met to consider changes to doctrine.宗教议会开会考虑更改教义。

9 strife   

n.争吵，冲突，倾轧，竞争

参考例句：

• We do not intend to be drawn into the internal strife.我们不想卷入内乱之中。
• Money is a major cause of strife in many marriages.金钱是造成很多婚姻不和的一个主要原因。

10 chaos   

n.混乱，无秩序

参考例句：

• After the failure of electricity supply the city was in chaos.停电后，城市一片混乱。
• The typhoon left chaos behind it.台风后一片混乱。

11 virtue   

n.德行，美德；贞操；优点；功效，效力

参考例句：

• He was considered to be a paragon of virtue.他被认为是品德尽善尽美的典范。
• You need to decorate your mind with virtue.你应该用德行美化心灵。