It is at this point that Leibniz produces the speculative postulate of his system.  Why not reverse the relation, and make the members represent the mind as the mind represents the members?  For then the unity of person represented in the mind will become something actual in the members also.

Representation appears to common sense to be a one-way sort of traffic.  If my mind represents my bodily members, something happens to my mind, for it becomes a representation of such members in such a state; but nothing happens to the members by their being so represented in the mind.  The [22] mental representation obeys the bodily facts; the bodily facts do not obey the mental representation.  It seems nonsense to say that my members obey my mind because they are mirrored in it.  And yet my members do obey my mind, or at least common sense supposes so.  Sometimes my mind, instead of representing the state my members are in, represents a state which it intends that they shall be in, for example, that my hand should go through the motion of writing these words.  And my hand obeys; its action becomes the moving diagram of my thought, my thought is represented or expressed in the manual act.  Here the relation of mind and members appears to be reversed:  instead of its representing them, they represent it.  With this representation it is the opposite of what it was with the other.  By the members’ being represented in the mind, something happened to the mind, and nothing to the members; by the mind’s being represented in the members something happens to the members and nothing to the mind.

Why should not we take this seriously?  Why not allow that there is two-way traffic—­by one relation the mind represents the members, by another the members represent the mind?  But then again, how can we take it seriously?  For representation, in the required sense, is a mental act; brute matter can represent nothing, only mind can represent.  And the members are brute matter.  But are they?  How do we know that?  By brute matter we understand extended lumps of stuff, interacting with one another mechanically, as do, for example, two cogs in a piece of clockwork.  But this is a large-scale view.  The cogs are themselves composed of interrelated parts and those parts of others, and so on ad infinitum.  Who knows what the ultimate constituents really are?  The ‘modern’ philosophers, certainly, have proposed no hypothesis about them which even looks like making sense.  They have supposed that the apparently inert lumps, the cogs, are composed of parts themselves equally inert, and that by subdivision we shall still reach nothing but the inert.  But this supposition is in flat contradiction with what physical theory demands.  We have to allow the reality of force in physics.  Now the force which large-scale bodies display may easily be the block-effect of activity in their minute real constituents.  If not, where does it come from?  Let it be supposed, then, that these minute real constituents are active because they are alive, because they are minds; for indeed we have no notion of activity other than the perception we have [23] of our own.  We have no notion of it except as something mental.  On the hypothesis that the constituents of active body are also mental, this limitation in our conception of activity need cause us neither sorrow nor surprise.