If, however, what we are talking about is a natural drive, then the character of nature as such namely, its character as a mechanism must be preserved along with the character of a drive; and hence the two must be synthetically united, which furnishes us with an intermediary element or middle term standing between nature as a mere mechanism (as well as the concept of causality) and freedom as the direct opposite of all mechanism (as well as the concept of substantiality), and we badly need something of this sort in order to explain the causality of freedom in nature.