  Why do quantum evolutions occur and why do they stop at certain points? In
classical thermodynamics affinity was introduced to predict in which direction
an irreversible process proceeds. In this paper the quantum mechanical
counterpart of classical affinity is found. It is shown that the quantum
version of affinity can predict in which direction a process evolves. A new
version of the second law of thermodynamics is derived through quantum affinity
for energy-incoherent state interconversion under thermal operations. we will
also see that the quantum affinity can be a good candidate to be responsible,
as a force, for driving the flow and backflow of information in Markovian and
non-Markovian 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 flow. 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 affinity.
