In answering this question we must first recognise that it assumes the existence of mental and physical states, which immediately supposes a dualist perspective. Material monist theories (e.g. functionalism) deny the existence of or reduce mental states to talk of physical states; whilst idealist monism denies the existence of the physical. Thus, neither of these perspectives can be used to answer this question.

The question references a particular theory of psychophysical causation known as parallelism. It is because psychophysical causation discusses whether mental states cause physical states or vice versa that a dualist perspective is required: a monist perspective does not allow for more than one state and thus there are no problems of causation.

Gottfried Liebniz (1646-1716) proposed parallelism. The theory acknowledges the Cartesian position that mental and physical substances exist, but asserts that there is no causal interaction between the two. Instead, God provides the apparent harmony between the mental and physical realms. Thus, although for every mental state there is a corresponding physical state, there is no causal relation between the two.

Liebniz's theory does not require God to intervene on each and every occasion to 'synchronise' the mental and physical states of individuals (this is known as occasionalism and was proposed by Nicholas Malebranche). Instead, Liebniz likens the process to two clocks being set by God such that they run at the same time, but do not influence each other. Once God has set the clock running, as it were, the parallel relationship has been created and continues onwards without further intervention.

Thinking of the two wheels of a bicycle provides a further illustration of this idea. Whilst in contact with the ground the two wheels move synchronously relative to each other, but do not have any influence over each other.

To understand the reasoning behind this theory it is useful to understand the context within which it was formulated. At the time (late 1600s to early 1700s) religion was a strong influence on all schools of thought. Invoking God in a theory was considered a strength, especially if it supported the existing orthodoxy, and in this case Liebniz reinforces God's role as creator. The religious influence also required the preservation of the concepts of consciousness and particularly the soul; hence dualist accounts of mind were favoured as these allowed for both.

Another considerable influence was the work of Descartes. In formulating the substance dualist account of mind in which the mind and body are different substances, Descartes had not accounted for how the two substances might interact. This was a significant problem for the dualist account of mind and parallelism can be seen as an attempt to circumnavigate this issue (as in parallelism the two do not interact).

In considering parallelism there are some plus points to the theory. The first is its intuitive appeal in preserving consciousness. Furthermore in bolstering dualism it appears to fit with our own internal experience of the differences between mental and physical states.

Secondly, parallelism builds upon and responds to the work of Descartes. Thus not only is the theory a step forward but also tackles and seemingly solves one of the key issues facing the Cartesian account of mind, that of interaction between the mental and physical substances. As parallelism does not require the two to interact the problem is avoided.

Finally, parallelism continues the Cartesian ethos of unifying science and religion. This was of tremendous significance at the time as the power of the church was absolute and scientific advance without their approval would have been difficult if not impossible. In reaffirming the idea that religion and science could co-exist philosophers such as Liebniz helped accelerate the rate of scientific progress.

However, some responses to the theory point to flaws with the argument. Firstly in responding to and building upon Descartes' work, Liebniz failed to account for the problem of location. As this was the other major problem facing dualist accounts of mind it could be argued that Liebniz's theory was incomplete, or at least fails to answer all of the questions.

Secondly, parallelism was attacked by applying Occam's razor: surely there are simpler explanations for interaction than some bizarre co-incidence? Liebniz anticipated this and explained that God set the mental and physical running in harmony. However, this in turn causes problems: the invocation of God is too convenient, it attempts to place the theory above reproach, the classic Deus ex machina. Furthermore in pre-supposing the existence of God, the theory now inherits all of the difficulties associated with proving God's existence.

In attempting to solve the problem of interaction, it can also be argued that Liebniz has merely deferred the issue. This is because although parallelism avoids the problem of interaction between mental and physical within the individual by simply denying that they interact, there is still a requirement for interaction between substances when God creates them in the first place. Thus the problem of interaction remains: how can one substance, even a divine one, interact with the other?

So, Descartes asserted that there was a natural interaction between the mind and body, Malebranche argued that this was not natural and God was required to intervene on every occasion. Liebniz took this forward by arguing that God could simply set things in synchronous motion as if they were interacting to begin with. However, given all these issues with interaction surely it might be simpler to argue for a monist theory? Even within the religious confines of the times Berkeley's idealist monism (where God creates everything in the mental realm and the physical does not exist) would seem more likely. More modern material monist accounts could also be used as attacks against parallelism, but only in the sense that they are arguments against dualism as an approach in the first place.

Property dualism provides a far more damaging attack on parallelism than comparison with other theories simply because it acknowledges the essential dual characteristics that Cartesian dualism seeks to capture whilst still offering an alternative. Property dualism argues that mental states are not reducible to properties of brain states but that they nevertheless remain entirely physical. Mental states are conjectured as emergent properties of physical matter that simply cannot be reduced to talk of physical properties. By construing both mental and brain states as physical properties this approach avoids the problems of interaction and (it can be argued) location. In addition this theory does not require the intervention of God, nor does it pre-suppose any particular belief structure.

Property dualism also provides answers to the issue of psychophysical causation (that parallelism originally sought to explain) in the form of epiphenomenalism. This theory explains how emergent mental properties are causally related to physical brain states by proposing an asymmetric relationship. Essentially brain states cause mental states, but the mental states in turn have no causal influence on the brain states or other physical properties.

However, whilst property dualism and epiphenomenalism provide a more modern and scientific approach to dualism they still suffer from their own issues that lead to more and more complex arguments being employed to defend the central position of mind and body as fundamentally and irreducibly different. Essentially dualist theories are contrived and lead to solipsism. They are at best fallback positions employed because other options are held to be unacceptable rather than complete explanations of the observed phenomena.

Thus, in conclusion to this assessment of the view that mental states run parallel to, but are not causally affected by physical states we can say that parallelism suffers from problems inherited from it's pre-supposition of dualism. Furthermore, even if dualism is assumed correct parallelism runs into problems by invoking God, in explaining the interaction between God and dual substances, and failing to account for the location of the mind.

Sources:

• Stanford encyclopaedia of philosophy entry for dualism - Howard Robinson
• www.dictionary.com
• An Introduction to the philosophy of mind - K. T. Maslin

Tutor: Oliver McAdoo MA

WWW www.arrod.co.uk