The last theory we are going to look at is Phenomenalism. We looked briefly at this in the last unit and, as you may recall, the theory proposes that we cannot experience anything beyond the phenomena of our perceptions. This view, similar to Idealism, states that our knowledge of reality must be based on what we actually perceive - on empirical evidence - otherwise, it is nonsense.

The most well known form of Phenomenalism is that proposed by the English philosopher A. J. Ayer and the movement known as Logical Positivism. From Ayer's viewpoint, a proposition is true only if some experience can verify it. So, the statement that the Amazon is the longest river in the world may be measured by looking at satellite photographs of all the world's rivers. However, the statement that "I can turn invisible but only when I close my eyes, no one is looking and there are no cameras, etc." is considered by Ayer to be nonsense because there is no possible way that anyone - even the 'invisible man' himself - can verify it. This is called the Verification Principle.

For Phenomenalists, all statements about the world are actually statements about sense experience - whether actual or possible. So, although we may not currently be able to prove that there has been life on Mars, it may in future be possible to do so. In this sense, whereas Idealists considered material objects not to exist, Phenomenalists consider them 'permanent possibilities of experience'.

Problems with Phenomenalism

Phenomenalism as a theory of truth is a form of reliabilism. What can be justified - or verified - has meaning, what cannot be - at least potentially - is nonsense. The methods used to verify statements are traditional empirical and scientific ones - i.e. the senses plus scientific equipment. As such, it is open to some of the same criticisms as reliabilism itself.

However, perhaps the main problem with the approach is that the verification principle itself is too vague. How is a statement verified?

Maths and logic are also problematic for this theory in that they are truths that seem to be independent of sensory verification. Ayer's answer to this was to consider them conventions of language. Similarly, all ethical and aesthetic statements were held to be neither true nor false because they could not be verified.

Ironically, one criticism points out that the verification principle itself is not - by its own criteria - meaningful. For, it is not an analytic truth (a 'convention of language') and neither is there any possible or actual sense experience that could be said to verify it.