Philosophers have long confronted the problem of "qualia". Few philosophers believe that it is possible to be sure that one person's experience of the "redness" of an object is the same as another person's, even if both persons had effectively identical genetic and experiential histories. In principle, the same difficulty arises in feelings (the subjective experience of emotion), in the experience of effort, and especially in the "meaning" of concepts. As a result, many qualitative psychologists have claimed phenomenological inquiry to be essentially a matter of "meaning-making" and thus a question to be addressed by interpretive approaches.