Psychophysical parallelism explained

Gustav Theodor Fechner
(1801-1887)

Theory of psychophysical parallelism states that mental and physical experiences occur simultaneously and are not necessarily bound by any causal interaction. The theory was established in the early 19th century by a German philosopher Gustav Theodor Fechner (who is also famous for Weber-Fechner law). While psychophysical parallelism definition might seem a bit unclear, the theory is very interesting and is one of few philosophical theories which have been accepted by numerous scientists. To better understand Fechner’s approach to mind-body problem a little historical background would be helpful.

In the middle of the 19th century, with a more and more rapid progression of scientific thought, many philosophers became interested in explaining the nature of mind and body interaction. This lead to a famous materialism dispute as the opponents of metaphysical philosophy gained many supporters (Vogt, Büchner, Moleschott). Materialistic approach to mind-body dichotomy was at that time seen as very radical, and some of its points still cause much controversy in the 21st century:

Gottfried Wilhelm von Leibniz
(1646-1716)

Thoughts issue from the brain just as gall is produced by the liver or urine by the kidneys.

Carl Vogt

Are our thoughts just like other bodily fluids which are generated in a similar way as numbers in computer programmes? Are we just very sophisticated machines? Gustav Fechner claimed to be able to give the solution to materialism debate. His theory, known as psychophysical parallelism, was first mentioned in 1820s but it was not until 1860 that his approach became widely known, thanks to his mature work Elements of Psychophysics.

There are many misconceptions about the meaning of psychophysical parallelism –  many people seem to confuse it with occasionalism, preestablished harmony and Cartesian doctrine of two noninteracting substances. You may read on other websites that psychophysical parallelism is a theory established by Leibniz. It is true that psychophysical parallelism is partially congruent  with Leibniz’s theory of noncausal conformity of the soul and the organic body. However, a very important difference is that Fechner rejected any theological grounds for his theory and therefore – even though psychophysical parallelism is a dualistic conception – by no means should it be confused with statements made either by Descartes or Leibniz. Fechner’s theory states that while mental and physical states are not causally dependent they are functionally dependent.

What does it mean? It means that to every mental event there is a corresponding brain event. It does not claim causal interaction, it does not deny it. It refrains from explaining the nature of mind and body. It is a very open and metaphysics-free theory. By many it is treated as a good and neutral foundation for more detailed explanations of the nature of mind and body problem albeit the theory itself does not answer many questions.

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