First, we do not now and never shall know precisely the particles of which the brain is composed (and still less their functions), or their different connections: on one side to the organs that receive impressions from objects, and on the other to all the parts of our body; second, our soul cannot exist without actually sensing itself; for these reasons, the soul has trouble in anributing to the construction of its body, which is actually unknown to it and which it does not consider, the effects that really depend on it.