are predicated in respect of what a thing is, it is necessary that the medium should be what it is, and a property in respect of properties, wherefore of two essential natures of the same thing, it will demonstrate the one, but not the other.
That this method then is not demonstration, has been shown before, but it is a logical syllogism of what a thing is, still let us show in what method this is possible, discussing it again from the beginning. For as we investigate why a thing is, when we know that it is, but sometimes those become evident at the same time, but it is not possible to know why it is, prior to knowing that it is, it is clear that in like manner the very nature of a thing or what it is, cannot be known, without knowing that it is, since it is impossible to know what a thing is, when ignorant if it is. We sometimes indeed know if it is, accidentally, knowing sometimes something belonging to the thing, as thunder we know, because it is a certain sound of the clouds, and an eclipse, because it is a cer-
