In the history of philosophy there have always been anti-realists who claim that all our perceptions are illusory. The more radical ones even doubt their own doubt, thereby rejecting any possibility of real knowledge. In the sphere of philosophy, they are referred to as skeptics. Would you please provide a brief but reasoned philosophic argument against their position?
Skeptics are of three persuasions. Some skeptics say that the only realities whose existence we may ascertain are ourselves and our thoughts; all else is an illusion. The more extreme skeptics go even further, claiming that the only reasonable position to hold regarding knowledge is solipsism: only I and my thoughts are definitely real. The most extreme, however, doubt even their own doubt. According to the latter, knowledge is impossible. The falsity of this position, however, is definitively demonstrated in epistemology.
We know without doubt and based on our God-given intuition that there is a reality independent of and external to us. Against the skeptics, we hold that there are many real objects, each one of which is distinct from all others and possesses properties peculiar to it.
Each external object can in the mind be described by two concepts: essence and existence. The absence of either of the two concepts means that the object in question is illusory. Assuming that John is a real human being, the concept of John in the mind can be the subject of two predicates: human being, as its essence, and existence, indicating its objective reality.
Both of these concepts are critical if we are to believe that John really exists. Nevertheless, the two concepts are fundamentally different. Existence is the negation of nonexistence, and as such the two cannot concur. The two contradictory concepts may, however, be alternatively predicated of a thing’s essence (in our case, human being as John’s essence).
Another issue in regard to the two concepts, essence and existence, is that they cannot both be exemplifiable by objective reality, for if they were, every object would be in effect two objects—which is absurd. For this reason, one of the two is truly objective (i.e., it has objective instances) while the other is applicable to external objects only through the mediation of the objective one.
In other words, one of the two concepts is a mere abstraction and as such is exemplifiable owing to its concomitance with the objective concept. So the question is: which of the two is objective? To answer this question, it suffices to notice that a thing possesses objective reality only when existence can be predicated of it; its essence in and of itself may or may not exist.
Thus, it is existence that is objective, not the essence of the object in question. Based on this argument, the correct philosophic position is that existence is the objective concept. As such, the other views—mainly, the opposite view that essence is objective and existences subjective—are false.
Another issue that merits mention here is the gradational [tashkiki] status of existence. But first let us point out that logicians identify two types of universals: 1) those that permit of various degrees [mushakkik], 2) those that are not such [mutawati]. The universals that are of the latter type are instantiated by objects that partake of that universal in question equally.
For instance, human being: all human beings are equally human beings, and if there are any differences between the various individuals of this class it is due to the extrinsic qualities (e.g., height, weight, age) that are not contained in the concept of human being. On the other hand, a gradational universal is that whose instances differ in their exemplification of the universal in question.
Such as light: there are brighter lights and there are less bright lights; they are all instances of light, but they differ in regard to intensity, although this difference itself arises from the essence of light not from any extrinsic quality. The majority of the sensory qualities are gradational: visual qualities such as light (as was mentioned), distance, dimension; auditory qualities, that is, the various sounds; olfactory qualities, that is, the various smells; gustatory qualities, that is, the various tastes; and finally the tangible qualities.
The difference that distinguishes the various instances of these qualities lies in their very essence, not in any extrinsic quality (one distance is shorter than another; one sound is louder than another; one smell is more pungent or more pleasant than another; one taste is more delectable than another; one object is softer or warmer than another).
Of course, on examination one will realize that there is a subtle point here. The intrinsic difference elaborated above does not arise from the mental concepts that constitute our thoughts, but rather from their exemplification that occurs in external objects.
For instance, the color black: the variations in blackness pertain to the existential instances of the concept, not to the concept itself. This demonstrates that tashkik (intrinsic gradation) actually pertains to existence, not to essence as such. In this light, we may affirm the truth of intrinsic gradational variation, although in existence not in essence.
Furthermore, those who deny the existence of intrinsic gradational variation based on the reasoning that a single entity cannot at once satisfy contradictory qualities are wrong in that they are confusing numeric singularity with generic singularity. Their reasoning is correct only in relation to numeric singularity, whereas in generic singularity the simultaneous application of contradictory qualities is possible.
From the foregoing discussion we can conclude that a mushakkik is an entity that allows of intrinsic variation so that the difference that distinguishes its instances derives from the very reality that unites them.
After having considered these preliminary points, we can now turn to the concept of existence. The concept of existence as such can be predicated of all objects. The reality of the concept of existence, its external instance, is the locus where objective reality and properties of things obtain.
The external reality of the concept of existence accommodates a variety of opposing qualities and states—necessity and contingence, cause and effect, unity and multiplicity, actuality and potentiality, etc.—and as such is a gradational entity [mushakkik] that subsumes a plurality of degrees that vary intrinsically in intensity. In this light, it becomes clear that those who hold the concept of existence to be ambiguous [mushtarak lafzi], reflecting the multiplicity of the essences of which it is predicated, are wrong. For, an essence is in and of itself neutral in regard to existence and nonexistence:
According to the definitive judgment of reason, both existence and nonexistence are predicable of an essence. Now, if the concept of existence were ambiguous, incorporating the meaning of the essence to which it is attributed (as our opponents claim) then to predicate nonexistence of an essence should constitute a contradiction—an obviously unreasonable conclusion. Their mistake arises from confusion between the properties of mental concepts and external objects, on the one hand, and from conflating the relation of essence with the reality of existence and the relation of essence with the mental concept of existence.
Another opposing view is that the concept of existence has two meanings: one pertains to the Necessary Existent and the other to contingent existents. This wrong position also stems from confusing the properties of concepts with those of external objects. The difference between the existence of the Necessary [wajib] Existent and that of contingent [mumkin] existents is not ideal but ontic.
There is another false view in this regard to the effect that external objects are fundamentally distinct realities. The problem with this view is that we meaningfully predicate existence of all objects while it is impossible to derive a single concept from multiple objects that have nothing in common.
Another topic pertinent to the discussion at hand is the relation of existence [wujud] to essence [mahiyyah]. As was explained above, we derive two concepts from every external object: one indicates its essence and the other its existence. Clearly only one of these two is directly exemplifiable while the other refers to reality through the mediation of the directly exemplifiable one. Considering that the ontic properties of an object relate to that aspect of it from which the concept of existence is derived, we can conclude that existence is the directly exemplifiable of the two concepts, the essence being a purely abstract concept.
Of course, this should not be construed to imply that a thing’s essence is an illusion that lacks any reference to objective reality. Rather, in saying that essence is an abstract concept, we mean that it is not immediately exemplified by external objects: its applicability to external objects is by means of existence, for a thing’s essence is its existential boundary that sets it apart from other objects.
Thus understood, the view that a thing’s essence is real only in the sense that is has objective instances is invalid. According to this view, the concept that comes into the mind and which we assume to portray truly the objective essence is merely an illusion. This line of reasoning runs in opposition to cogent philosophic arguments that prove that a thing’s essence that is reflected in the mind is essentially identical with the ontic essence of the object in question. It is for this reason that we are able to form true propositions by placing the essences reflected in the mind as subjects and then describing them.
In addition, if we concede that the essences reflected in the mind are merely subjective impressions, the hypothetical propositions formulated in various sciences would be doomed; even worse, any science that posits universal propositions should, on the basis of this conception, be discarded as chimerical. The physician would be wrong to assert that every human being has a heart. One would be justified only in uttering propositions that are confined to the objects one has directly observed. This position, however, would mean that all sciences should be forsaken.
Another consequence of this conception is that such logical definitions as species, differentia, substantial, accidental, etc. that we predicate of essences would also lose credibility.1 Those who thus reject the validity of essences hold that such concepts are merely images of external objects similar to a picture one draws of something. The picture does not in any way define the object in question; it only reminds us of it. The falsity of this position, however, is very clear. For, if we have no way to truly perceive the external object, how can we tell that a certain image depicts the external object in question. Thus, we can condemn this conception as a blatant form of skepticism.