the
nature either of things or of mind. Their function is only to indicate
what things are useful or hurtful to our composite nature as such, or
in other words what things tend to confirm or dissolve the unity of
mind and body. They indicate that _something_ is taking place in our
body, or without it, and so stimulate us to some kind of action, but
_what_ it is that is taking place they do not tell us. There is no
resemblance in the sensation of pain produced by great heat to the
rending of the fibres of our body that causes it. But we do not need
to know the real origin of our sensation to prevent us going too near
the fire. Sensation leads us into error only when we are not conscious
that its office is merely practical, and when we attempt to make
objective judgments by means of its obscure and confused ideas, e.g.
when we say that there is heat in our hands or in the fire. And the
remedy for this error is to be found simply in the clear conviction of
the subjectivity of sensation.

Theory of occasional causes.

These views of the nature of sense, however, at once force us to ask
how Descartes can consistently admit that a subjective result such as
sensation, a result in mind, should be produced by matter, and on the
other hand how an objective result, a result in matter, should be
effected by mind. Descartes explains at great length, according to his
modification of the physiology of the day, that the pineal gland,
which is the immediate organ of the soul, is acted on by the nerves
through the "animal spirits," and again by reaction upon these spirits
produces motions in the body. It is an obvious remark that this
explanation either materializes mind, or else puts for the solution
the very problem to be solved. It was therefore in the spirit of
Descartes, it was only making explicit what is involved in many of his
expressions, when Geulincx, one of his earliest followers, formulated
the theory of occasional causes. The general approval of the Cartesian
school proved that this was a legitimate development of doctrine. Yet
it tore away the last veil from the absolute dualism of the system,
which had so far stretched the antagonism of mind and matter that no
mediation remained possible, or what is the same thing, remained
possible only through an inexplicable will of God. The intrusion of
such a _Deus ex machina_into philosophy only showed tha