The virtual distinction, on the other hand, although it also, as an object of thought, is only an _ens rationis_—inasmuch as there is no real duality or plurality corresponding to it in the reality into which the mind introduces it, this reality being a real _unity_—the virtual distinction is considered, nevertheless, to have a ground, or reason, or foundation (for making and introducing it) in the nature of this one reality; that is, it is regarded as having a _real_ foundation, a _fundamentum in re_. In so far, therefore, as our knowledge is permeated by virtual distinctions, reality cannot be said to be _formally_, but only _fundamentally_ what this knowledge represents it to be. Does this fact interfere with the objective validity of our knowledge? Not in the least; for we do not ascribe to the reality the distinctions, and other such modes or forms, which we know by reflection to be formally characteristic _not of things_ but _of our thought or cognition of things_. Our knowledge, therefore, so far as it goes, may be a faithful apprehension of reality, even though it be itself affected by modes not found in the reality. But what is this _real_ foundation of the virtual distinction? What _is_ the _fundamentum in re_? It is not a real or objective duality in virtue of which we could say that there are, in the object of our thought, two beings or realities one of which is not the other. Such duality would cause a _real_ distinction. But just here the difficulties of our analysis begin to arise: for we have to fix our attention on actually existing realities; and, assuming that each and every one of these is an individual, we have to bear in mind the relation of the real to the actual, of reality as abstract and universal to reality as concrete and individual, of the simple to the composite, of the stable to the changing, of essential to accidental unity—in any and every attempt to discriminate in detail between a real and a virtual distinction. Nor is it easy to lay down any general test which will serve even theoretically to discriminate between them. Let us see what grounds have been mainly suggested as real foundations for the virtual distinction.