1.1 May the First Principle of things grant me to believe, to understand and to reveal what may please his majesty and may raise our minds to contemplate him.

1.2 O Lord our God, true teacher that you are, when Moses your servant asked you for your name that he might proclaim it to the children of Israel, you, knowing what the mind of mortals could grasp of you, replied: "I am who am," thus disclosing your blessed name. You are truly what it means to be, you are the whole of what it means to exist. This, if it be possible for me, I should like to know by way of demonstration. Help me then, O Lord, as I investigate how much our natural reason can learn about that true being which you are if we begin with the being which you have predicated of yourself. 1.3 Although being has many properties it would not be irrelevant to consider, it is to the more fruitful source of the essential order that I turn, proceeding according to the following plan. I shall set forth in this first chapter the four divisions of order. From this one can gather how many kinds of essential orders exist. 1.4 For a division to be clear it is necessary (1) that the members resulting from the division be indicated and thus be shown to be contained in what is divided, (2) that the mutually exclusive character of the parts be manifest, and (3) that the classification exhaust the subject matter to be divided. The first requirement will be met in this chapter; the others, in the second. With no attempt at justification, then, in the present chapter I shall simply enumerate the divisions and explain the meaning of the parts. 1.5 I do not take essential order, however, in the strict sense as do some who say that what is posterior is ordered whereas what is first or prior transcends order. I understand it rather in its common meaning as a relation which can be affirmed equally of the prior and posterior in regard to each other. In other words I consider prior and posterior to be an adequate division of whatever is ordered, so that we may use the terms order and priority or posteriority interchangeably. 1.6 First Division: In the first place then I say that the primary division of essential order appears to be that of an equivocal term into its equivocates, namely into the order of eminence and the order of dependence. 1.7 In the first, what is eminent is said to be prior whereas what is exceeded in perfection is posterior. Put briefly, whatever in essence is more perfect and noble would be prior in this manner. It was this kind of priority Aristotle had in mind in his proof that act is prior to potency in the ninth book of the Metaphysics where he calls act prior according to substance and form (species). "The things that are posterior in becoming," he declares, "are prior in form and in substantiality." 1.8 In the second type of order, the dependent is said to be posterior whereas that on which it depends is prior. I understand prior here in the same sense as did Aristotle when in the fifth book of the Metaphysics, on the authority of Plato, he shows that the prior according to nature and essence can exist without the posterior, but the reverse is not true. And this I understand as follows. Even though the prior should produce the posterior necessarily and consequently could not exist without it, it would not be because the prior requires the posterior for its own existence, but it is rather the other way about. For even assuming that posterior did not exist, the existence of the prior would not entail a contradiction. But the converse is not true, for the posterior needs the prior. This need we can call dependence, so that we can say that anything which is essentially posterior [in this way] depends necessarily upon what is prior but not vice versa, even should the posterior at times proceed from it necessarily. These could also be called prior and posterior according to substance and species, as were the others above, but to be more precise, let them be called prior and posterior according to dependence. 1.9 Second Division: Leaving the order based on eminence undivided, I subdivide the order of dependence, for either the dependent is something caused and that upon which it depends is its cause, or the dependent and that upon which it depends are both the result of the same cause, the former more remotely, the latter more proximately. 1.10 Patent enough is the meaning of the first member of this second division and the fact that it falls under the heading of an essential order of dependence. For it is clear not only what cause and caused are but also that the two are so related that the caused depends essentially upon the cause and the cause is that upon which it depends as something prior in the sense explained above.

1.11 But the [sense] of the second member of this second division is not so self-evident; neither is it immediately clear just how it fits under the notion of essential dependence. Its meaning is explained as follows. If one and the same cause produces a dual effect, one of which is such that by its nature it could be caused before the other and therefore more immediately [e.g. a subject like mind or matter], whereas the second can be caused only if the first is given [e.g. some quality or modification of the subject such as a state of mind or the shape or form of matter], then I say that the second effect is posterior in the order of essential dependence whereas the more immediate effect of the same cause is prior. Such is the meaning of this member. 1.12 From this I proceed to show secondly that this member pertains to the category of essential dependence. In other words there is an essential dependence of the more remote upon the more proximate effect. First of all, the former cannot exist without the latter. Secondly, the causality of their common cause affects them according to a certain order, and they in turn are ordered to one another essentially in virtue of their respective individual relations to a mutual cause. Thirdly, the latter as such need only be considered the immediate cause of the more proximate effect. If the latter is non-existent, this common cause is regarded as only remotely responsible for the rest of the effects, whereas it is considered to be their proximate cause once the first effect has been caused. Now no effect follows exclusively from a remote cause as such. Consequently the second effect depends on this cause as having given existence to the first effect and therefore this second effect also depends upon the existence of the more proximate effect. 1.13 Third Division: Both parts of this second division are further divided. I will subdivide the second member first because it is in line with what we have just been saying. For a more immediate effect is called prior not only when it proceeds more proximately from the immediate cause of the two effects, but also when the common cause is related more remotely to an effect. Suppose the proximate cause of one of the effects, A [e.g. the state of mind], is in no way a cause of the other effect. B [i.e. the mind itself], but some other prior cause is both B's immediate cause and the remote cause of the other's immediate effect, [Al. In such a case there would still be an essential order based on a priority and posteriority of effect so long as the causality of their common cause is itself related to these effects by an essential order. 1.14 That the second member of this division is an instance of the order of essential dependence is not so evident at first sight, but it may be proved in this fashion. Since each effect is essentially ordered to some common third which is their mutual cause, it follows that these effects are also essentially ordered to one another. Then too, the common cause is only a kind of remote cause of the posterior if the prior effect is not produced. Moreover, the posterior effect cannot exist without the prior. 1.15 Fourth Division: The cause mentioned in the first part of the second division is in turn divided into the famous fourfold classification of final, efficient, material and formal cause, which need no explanation. The posterior correlative to cause is subject to a corresponding division, namely (1) that which is ordered to an end—for the sake of brevity we shall call it finitum; (2) the effect; (3) what is made from matter—we may call it the materiatum; (4) what is given form—we may call it the formatum. The meanings of these divisions I shall skip for the present since I have treated them elsewhere at length and shall subsequently touch on them again as circumstances dictate. 1.16 To sum up the fruits of this chapter, we can say that the essential order is exhaustively divided by breaking it down into six orders. Four of these express a relationship between a cause and that which is caused; another represents an order between two things that are caused (we include here under a single heading the two members of the third division); one is the order between something eminent and what is less perfect. 1.17 Two things remain to be proved before our presentation of these divisions is complete, namely, that the parts of each division are mutually exclusive and that they exhaust the subject matter to be divided. In so far as it is necessary for our purpose, we shall deal with these points in the following chapter, wherein certain necessary propositions of a general nature will be proposed and the interrelations of the aforementioned orders will be studied with a view to discerning any necessary entailments or lack thereof that may exist between them, for all this has a great bearing on what will follow.