More of Wittich’s Anti-Spinoza: the Criticism of Ethics, Part 1, Definition 3
Definition 3: By substance I understand that which is in itself and conceived by itself; that is, that whose concept does not require the concept of another thing from which it must be formed.
The author can here be observed committing the same error as we have already noted in Definition 1, namely second notions are considered in abstraction from their particulars, before their particulars are grasped. In this way it comes about that we really grasp a shadow and do violence to human thought, since all people understand by substance a particular thing among extant things — God, a mind, a body. Considering in these particular things that which is real  they find infinite thought in God, finite thought in the mind, and extension in the body. But now a philosopher meditates in his soul, and reflects that all these (infinite thought, finite thought, and extension) are real and extant, as they are understood by themselves and alone and represented in ideas such that there is nothing else in them from which they could be taken away. He then understands such things alone to subsist in full form and thus calls them substances, thus forming the abstract notion of substance, which is a thing that is understood by itself and alone, and so is by itself in that there is nothing from which it could be taken away.
But this notion, as is apparent from this statement, is not understood clearly enough unless the mind refers to one or other of the particulars. Our mind must grasp some particular by this notion, lest it falter and take the notion for an existing thing, thus mistaking the shadow for the body.
And this notion of substance strictly and properly speaking will be abstract and aptly understood in this way. And it will be distinguished from substance taken widely, since others are included in substance taken widely. For some thing either is really by itself, as God, the mind, the body, or as our mode of considering it, as a square shape, motion, etc. Where we have some certain form, nature, or essence, this is equivalent to substance taken widely, since substance taken widely is the same as the essence of some thing: ousia, as Aristotle said — form, or nature. Thus a figure is a substance taken widely, but must be called an accident if compared with a substance strictly accepted.
Now by this definition of Spinoza we are in the end led, as is later shown, to there being but one substance, God; all other beings are modes of this substance. Without doubt this defines substance strictly speaking. But here it is helpful, in order to understand the matter most distinctly, and so that we can distinguish the notion of substance from a thing that is substance, to attend to the origin of these abstractions and the name brought about by such abstraction. Substance, if we attend to the origin of the words, is named from stare, which is to subsists of itself, and from the preposition sub. It thus signifies that which subsists of itself and is the subject of another, which does not stand by itself and therefore is called accident. 
But since substance is called being by itself, this being must be properly unpacked. But this, the word Is, is in its first and simplest signification only said about a thing by which we are affected in our soul, which is nothing other than the first act of will or affirmation, which posits nothing in the thing that was not first under the intellect. Thus the will does not know or embrace anything that the intellect does not propose to affirm and know without confusion and obscurity. And so to the idea in the intellect is added the act of will, which knows what the intellect reveals in the idea. This recognition of the will is the first meaning of the word Is.
But this is very general and common, since it is used of apparent things, of thoughts, and of things existing outside of thought. When applied to thoughts and apparent things, as when I say heat is or pain is, the idea is considered in its actual rather than representative being, as something in my mind — some act in my intellect, and this is the sense of these propositions. That idea, which represents something to me, which I call either pain or heat, is really in my intellect. And so the will only accedes to what is in the intellect itself and does not refer what is grasped in the intellect to what is outside the intellect.
But when it is used for what is outside the intellect, the idea is considered in its representative being and insofar as it supposits for the thing it represents, as when I say a Triangle is or a Body is. Here it is not only a triangle or body in thought that is signified but beyond this a triangle or body outside of thought — an extant thing (since the idea of a triangle or body in thought represents something outside thought). Again the word Is again signifies nothing other than the act of the will, which grasps that which the intellect represents, but here it grasps it not with a relation of existence to the intellect, but with a relation of existence outside of it. And thus, when I say a triangle or a body is, I mean that to these ideas, which I have in my intellect, something answers that is not in the intellect itself but outside of it.
But now this existence outside the intellect is again distinguished. For one idea represents it so that we can call it being by itself; the other so that we can call it being in another.  And this being by itself is what constitutes the nature of substance strictly speaking, while being in another can have its place among substances broadly taken. Therefore when something exists outside the intellect so that it is in itself and not in another, thus does not depend on another as a subject, it is called being by itself. In this way what is by itself is not in another, and not from another, nor depending on another as its subject. This we can call authuparxia.
But we must not be dragged further to conceive of substance as depending on no other thing as a cause, which is the sense in which Spinoza has accepted this definition. This is shown from this: that he tries in what follows to show God to be the only Substance, while created things are only various modes of this substance. Also we can read this in the Treatise on the Emendation of the Intellect, p.386: “If a thing is in itself, or as the vulgar say, cause of itself then it should be understood only by its essence. But if a thing is not in itself, but requires a cause to exist, then it should be understood by its proximate cause.”
It was not right, however, to take these phrases, in itself and by itself in a completely different sense from that in which others are accustomed to use them. In any case, those things that are extant outside the intellect are either in another subject, or are not in another subject but rather in themselves, or are such that no extrinsic cause for them can be found and their own nature and greatest power suffices for their existence. Surely these three can be distinguished by nature, and consequently the third should no more be confused with the second than the second with the first, contrary to what Spinoza has done. The first is that commonly called accident, the next is substance, the third is given the name uncreated and independent substance, and is not to be confused with created substance.
Without doubt, therefore, the idea that Spinoza has of substance is feigned, thus according to the ideas philosophised in the Treatise on the Emendation it will not be true, so that this definition of substance in the sense Spinoza accepts it does not express a true idea and consequently will not be a true definition. Will this then be the principle and foundation upon which we will build the structure of demonstrations and many truths? A true definition, according to Spinoza himself, as we have seen in the preface (On the Method of Demonstration), must have a determinate object. Nor does it suffice that someone should say he wants to understand something by some word that departs from common use. Nor truly is it permitted, when one inquires  into things that are really found in nature, to understand words by which people commonly express and signify things to mean something different from what they normally understand them to mean, unless somebody wishes to be counted among those people who sweetly philosophise, not about things that are in the world, but about the figments of their own brains — that is, who are delirious.