The word 在乎 is formed through a conceptual fusion where the first character 在, meaning "to be at" or "to exist in", establishes a sense of location or state. This is combined with 乎, an ancient particle that originally functioned to express inquiry or exclamation, but here extends the meaning into a abstract, relational sphere. Together, they create a metaphorical space of "being within the realm of caring about", transforming the literal idea of physical presence into the figurative and emotional state of "to mind" or "to care about". The formation is less about adding two concrete meanings and more about using 在 to anchor an attitude and 乎 to project that attitude onto something external, resulting in a single concept of invested concern.