A more radical slant on the mind-body problem was presented by the Jewish-Dutch philosopher Baruch Spinoza (1632 – 1677) who argued that there were not really two substances, but two attributes of the same substance. Thus reality was therefore a case of two perspectives on the same thing: physical matter as perceived through the senses and mental stuff as experienced with the mind.

The problem here is that it leaves the nature of this common substance undefined. If matter and mind are only attributes of it, what then is it? Another problem is that the theory requires that mind and body correspond – and yet, is this the case? Things seem to happen in the body that the mind is not aware of, nor can we really say whether there is always a corresponding mental process for every physical one.