(a refutation of Berkeley’s Subjective Idealism)
Idealism, as opposed to Realism, views the world as a mental construct (where the world is the sum of all objects and these objects are not of matter, but of ideas). Berkeley’s Subjective Idealism holds the same and considers the mind of man as paramount in knowing that objects (that are of ideas) exist. In this philosophy, matter is viewed as non-existent; objects are just the collections of sense data (that are not material) in those who perceive them.
The usual example that I use in explaining Berkeley’s philosophy is the perception of a ball. Let us say I am seeing a ball and in seeing it, I might infer that I am indeed seeing the ball itself. With this theory, it would be argued that in my perception of the ball, what is observed is the idea of the ball in my mind and not the ball itself. Berkeley would say that it is impossible for me to compare the ball itself to my idea of it since what I can only observe is my idea of the ball. Hence, what we can only verify and claim as existents are the ideas and not the material objects themselves. In this case, material objects do not exist in their own right; they are just products of the mind. In our assumption of their existence, we infer that they indeed exist and that they and our ideas of them in our minds have a necessary connection.
Berkeley’s arguments make a lot of sense. It accounts the limit of the human mind and its inability to verify the existence of matter. Furthermore, it challenges the self – evidence of the existence of a material world and offers a possibility that an external world may not be a material world. However, though it could be argued that some philosophies are merely assuming that material objects exist without giving proofs because they are pointing to the self – evidence of their existence, Berkeley’s arguments also tends to be fallacious. It somehow commits argumentum ad ignorantiam as it claims that matter does not exist because it cannot be verified. Berkeley himself jumped into a conclusion that he himself cannot fully prove; inability to verify the material object’s existence does not imply its non-existence.
There also seems to be a problem in his rejection of Locke’s view regarding primary and secondary qualities. He argues that since it is the ideas, and not the material objects that consist reality, the qualities of the material objects exist only in the mind. There is nothing, according to him, that is in the object but what is perceived. Once objects are perceived, they are perceived; there is no distinction between primary and secondary qualities. The example that I used in my essay in supporting the distinction between primary and secondary qualities is that of the blood. Blood as perceived is red in color; but with a thorough investigation, we would understand that the blood appears only as red because of the oxygen present in it. Through looking at a microscope, we could not see the redness of the blood as how our naked eyes see it; what we can only see in the microscope are tiny particles that are not red in color. There must be a recognition that the redness of the blood is not in the blood itself. It must be taken into consideration that primary qualities of the blood (or those that are of the blood itself) must be different from the secondary qualities of it that is dependent on how the object is perceived (what our naked eyes see is not what the object itself possesses).
Furthermore, if objects are not composed of matter, then where are the ideas of these objects based? Surely, it may be argued that ideas may be based from ideas (that the ideas I have in my mind is based on the ideas existing outside of me). However, if the ideas in my mind are based on ideas that exist in the external world, then we could also ask ourselves on how we can be able to verify whether these ideas have true likeness to the ideas where they are based. It commits the same problem that Berkeley noticed in the view that ideas are based on the existence of material objects that are outside of us. Here, we could observe that problem lies in naming. Others hold that idea in the mind is based on matter; Berkeley holds that idea in the mind is based on idea. If we will clearly look at the arguments, they are just the same; both hold that the ideas in the mind are based on the external world. It is just that Berkeley wished not to call the existents in the external world as material (as Science claims). The problem lies on language; the problem is whether those we wish to perceive or those that exist in the external world would be called matters or ideas. There is no point in debating whether the external world is material (composed of matter) or Ideal (composed of ideas) because we cannot speak of those that we cannot verify.
Berkeley’s arguments also imply that existence is an accidental property of an object; that it exists because it is perceived. It contradicts that existence is an essential property of an object. Claiming that existence is merely an object’s accidental property would lead to absurdity. If existence is already an accidental property, then there is nothing in the object that is essential. An object will not have properties (though it may have potentialities; but potentialities are not properties of the object) if it does not exist. Furthermore, existence is not a property that is a predicate of an object. The object is its existence. Hence, its existence cannot be merely accidental such that it exists because it is perceived. We cannot take away from an object its right to exist on its own.
My arguments imply Realism and might be considered as a support of Kant’s concept of noumena (as obvious in footnote 3 of this essay). Berkeley could have asked me as to how the unperceived (the noumena) exist. How could those in the external world exist if I cannot perceive them? I would point out that there are those in things that we cannot perceive though we can be certain (in principle) that they exist. We know that infinity exists. In principle, we can understand infinity; we can know infinity by its being infinite though we cannot know and perceive the whole of it. If objects have this infinity then it is most likely that objects have something that we cannot actually know. Let me use a dog as an example. If we are to dissect a dog, we could observe its parts or organs. We could further observe that these organs are composed of tissues, tissues of cells, cells of DNA, until we reach the littlest thing that we could observe or the atom. Scientifically speaking, atom is the most basic unit of a thing, but science also recognizes that atom has parts (protons, neutrons and electrons). Science does not deny that atom is still divisible into fragments (in fact, nuclear fission proves that atomic nuclei are divisible into fragments). In principle, we could understand that the parts of the atom are consisted of tiny particles that we could not observe and the tiny particles are still composed of smaller particles, etc. Here, we could observe that there is infinity in a thing and we cannot perceive and know the whole of it even though we can recognize its infinity. We could infer from here that there are those that exist even if they are beyond our perception.
There are still more in Berkeley’s philosophy that I wish to explore. However, what has been written is already enough to challenge Berkeley’s epistemology using Subjective Idealism. I would no longer question his assumption of the existence of a Grand Perceiver nor elaborate more on my previous arguments. I would not even discuss here my view regarding reality and external world. These would require another course of enquiry. The purpose of this essay is simply to provide a critique on Berkeley’s epistemology.
 My essay “Objectivity of Reality of the external world” tried to refute Berkeley’s subjective idealism in proving that an external world, which is material, “exists even when there is no mind to perceive it and even if I cease to exist”. The essay also claims that “reality exists independently of the human mind and that there can be no other world or realities than this one”.
 The ball itself and the idea of the ball are not the same; the ball itself points to an object existing in the outside world while the idea of the ball points to an object existing in the mind.
 There is a futility in perplexing ourselves whether external world is material or Ideal if we are to recognize that we cannot verify them. All that we can only verify and thus speak of are those that exist in our minds. If an external world exists (whether it is material or not), we cannot be sure whether our perception of it is the same with how it exists. This, however, does not mean that Berkeley’s argument is absurd. This simply points out that there seems to be a vicious cycle in perplexing ourselves with this problem.
 The term ‘challenge’ is more appropriate than the term refute