According to Henri Bergson, the representations we make of time and matter, since ancient times result from our vital needs. The divisions (in seconds or minutes, in substances or objects) are abstractions we create to control reality, but the essence of reality is pure continuity. In this paper, we will introduce a capital concept in Bergson’s philosophy, duration (I), and analyze its nature as a qualitative multiplicity (II). Next, we will study the problems “classical metaphysics” has incurred in conceiving the different manifestations of duration as a quantitative multiplicity, and not as a qualitative multiplicity (III). Finally, we will see how these mistakes depend on the way in which the human being perceives reality, in order to act and cooperate (IV). It is the purpose of this paper to demonstrate that, according to Henri Bergson, reality is essentially duration, i.e., pure continuity.