Phenomenalism

In the philosophy of perception, phenomenalism is the view that physical objects, properties, events (whatever is physical) are reducible to mental objects, properties, events. Ultimately, only mental objects, properties, events, exist. In particular, we may reduce talk of physical bodies to talk of bundles of sense-data.

The philosopher who is most famous for advocating both the bundle theory of objects, and phenomenalism, is the 18th century Irish philosopher, George Berkeley. Berkeley's version is more commonly called "subjective idealism".

Philosophers who hear the sceptic's challenge – "There's no reason to think an external world exists" – reply, "Well, no, I guess there isn't any reason to think that an external world exists. All there is, is sense-data. Physical objects are bundles of sense-data. When I hold up my hand, and I see it, I'm not seeing something external to my mind; I'm seeing a series, a whole bundle, of hand sense-data, and there is no hand apart from those hand sense-data. That's what my hand is – a bundle of sense-data." Such philosophers get around scepticism not by replying to the sceptic and proving the existence of an external world, but instead by saying that there is no external world.

One objection to phenomenalism, uses a reductio ad absurdum. Suppose the phenomenalist is correct. This argument intends to disprove that assumption.

Let's assume that, for me, the physical world is all just a construction out of my sense-data. Now suppose you and I are talking about philosophy. On the face of it, there's my body, and my mind associated with it, and there's your mind, with your body associated with it. But we are assuming that phenomenalism is true. That means that when I see your body, I'm not seeing an irreducibly physical body; I am seeing a bundle of sense-data in my own mind. Let's suppose I hear you saying all sorts of intelligent things, which I want to take as evidence of the existence of your mind, of what you are thinking. All those intelligent things you say are, after all, sense-data in my own mind. So I have no reason to think that either your body, or your mind exist. The phenomenalist has no reason to believe that any other minds, besides his own, exist.

Why should the phenomenalist be surprised when we say that? After all, phenomenalism denies that an external world exists. Just remember what "external world" means according to the phenomenalist: it means the world outside his own mind. But that means that all other bodies and other minds are part of the external world. The phenomenalist seemingly must come to a counterintuitive conclusion. The argument in brief:

1. If phenomenalism is true, then nothing that is thought to be in the external world exists.
2. But other minds besides my own are thought to be in the external world (since the external world is anything outside my own mind).
3. Therefore, other minds do not exist.

The phenomenalist ends up a solipsist, taking the view that one's mind is the only thing that exists – that one is entirely alone in a universe that exists completely in one's own mind. Berkeley got around this by employing God and his revelation through the Bible. However, phenomenalism was also adopted by Schopenhauer, who was atheist (or, arguably, a pantheist, since his Will has some divine properties, such as omnipotence, and is responsible for the existence of the representation). Schopenhauer argued that there was also the flip side of one's perception ["representation" as he called it] which is found through intuitive knowledge. He identified this flip side of perception as being will and he claimed that one could see the same inner-nature in other people [as well as other animals and all beings] only after one has acknowledged the will in oneself. The above argument invites critique from another direction by assuming that we have firsthand sensory knowledge of our own minds. If we reject that assumption then our own minds and the minds of others are on the same ontological footing, since we can confirm the existence of neither through sense-data, strictly speaking. A straightforward charge of solipsism then becomes difficult.

Another classic problem is that if there is a book on the table before you and you turn around, you do not know whether it is there or not; this seems to offend common sense. Berkeley solves it by saying that God is everywhere, and Schopenhauer by saying that the will dwells in all our perceptions. A simpler response might be to ask, what would you think if you turned back around, only to see that the book was gone? Would you assume it has been stolen or destroyed by someone else? And if you assumed as much, would your lack of knowledge regarding the book's continued existence count as evidence for or against phenomenalism?

Despite the inclination to reject solipsism out of hand, its argument is made in such a way that it is that it is not falsifiable and therefore cannot be disproven; at least not by means of modern science, philosophy included. By extension the above argument does not disprove phenomenalism in any way, even if we do accept that phenomenalism is solipsistic. A lack of falsifiability would render phenomenalism unscientific, however, so one could potentially reject it on that basis instead.