78. These principles have given me a way of explaining naturally the union or rather the mutual agreement [conformite] of the soul and the organic body. The soul follows its own laws, and the body likewise follows its own laws; and they agree with each other in virtue of the pre-established harmony between all substances, since they are all representations of one and the same universe. (Theod. Pref. 340, 352, 353, 358.)

这些原理给予我一种方法，可以自然地解释灵魂和有机形体之间的结合或一致。灵魂遵循自身的法则，形体也遵循自身的法则；凭借所有实体间的前定和谐，两者之间能够协调一致，因为它们都是同一宇宙的表象。（参见《神正论》前言，第340节, 第352节，第353节, 第358节）

79. Souls act according to the laws of final causes through appetitions, ends, and means. Bodies act according to the laws of efficient causes or motions. And the two realms, that of efficient causes and that of final causes, are in harmony with one another.

灵魂按照目的因通过欲求、目的和手段的法则而活动。形体依据动力因的或运动的法则而活动。这两个领域，目的因的领域和动力因的领域，是彼此协调的。

80. Descartes recognized that souls cannot impart any force to bodies, because there is always the same quantity of force in matter. Nevertheless he was of opinion that the soul could change the direction of bodies. But that is because in his time it was not known that there is a law of nature which affirms also the conservation of the same total direction in matter. Had Descartes noticed this he would have come upon my system of pre-established harmony. (Theod. Pref. 22, 59－61, 63, 66, 345－348, 354, 355.)

笛卡尔认识到，灵魂不可能给予力量于形体，因为在物质中力保持相同的数量。然而他却认为，灵魂可以改变形体的方向。但这是因为在他的时代，物质中运动方向的守恒这一自然律尚不为人所知。如果笛卡尔知道这一点，他一定会赞同我的前定和谐体系。（参见《神正论》前言，第22节, 第59－61节，第63节，第66节，第345－348节，第354节，第355节）

解释：

笛卡尔一方面把形体与灵魂割裂开来，另一方面又试图想办法使其相连系，以解释身心互动的经验事实。他认为，尽管灵魂不可能改变形体运动的数量，因为物质中运动量是守恒的，但灵魂可以通过大脑中的松果腺的中介而改变形体的运动方向。与之针锋相对，莱布尼茨认为，不仅物质运动的数量是守恒的，而且其运动的方向也是守恒的，从而物质运动完全是自足的，不需要也不允许灵魂的干预。通过将笛卡尔的动量守恒定律改造成动力守恒定律，莱布尼茨为其前定和谐理论提供了物理学的基础。

81. According to this system bodies act as if (to suppose the impossible) there were no souls, and souls act as if there were no bodies, and both act as if each influenced the other.

根据这一体系，形体就象不具有灵魂那样（这当然是不可能的）活动，灵魂就像不拥有形体那样活动，这两者就像能相互影响那样活动。

解释：

后来的笛卡尔主义者如马勒布朗士等，放弃了笛卡尔的困难重重的身心直接相关联的理论，提出了“偶因论”（occasionalism）来解释身心关系。他们认为，灵魂和身体之间不存在真正的因果关系和相互作用，只是由于上帝的随时干预，才使得身心之间保持协调一致。莱布尼茨的前定和谐理论与偶因论有相同的地方，即都认为身心间不可能有真正的关联；两者的不同在于，偶因论依赖于上帝的随时干预来保持身心间的协调，前定和谐理论则认为，上帝之在创始之初规定形体的规律与灵魂的规律协调一致，此后上帝就不再进行任何干预了。莱布尼茨认为，偶因论者实际上把上帝变成了个糟糕的钟表匠，需要不断的调整，才能让他所造的形体和灵魂这两块表保持时间的一致。