Why do quantum evolutions occur and why do they stop at certain points? In classical thermodynamics afnity was introduced to predict in which direction an irreversible process proceeds. In this paper the quantum mechanical counterpart of the classical afnity is found. It is shown that the quantum version of afnity can predict in which direction a process evolves. A new version of the second law of thermodynamics is derived through quantum afnity for energy-incoherent state interconversion under thermal operations. we will also see that the quantum afnity can be a good candidate to be responsible, as a force, for driving the fow and backfow of information in Markovian and nonMarkovian evolutions. Finally we show that the rate of quantum coherence can be interpreted as the pure quantum mechanical contribution of the total thermodynamic force and fow. Thus it is seen that, from a thermodynamic point of view, any interaction from the outside with the system or any measurement on the system may be represented by a quantum afnity.
