  We propose an alternative framework for quantifying coherence. The framework
is based on a natural property of coherence, the additivity of coherence for
subspace-independent states, which is described by an operation-independent
equality rather than operation-dependent inequalities and therefore applicable
to various physical contexts. Our framework is compatible with all the known
results on coherence measures but much more flexible and convenient for
applications, and by using it many open questions can be resolved.
