In many different cultures and times, nature has been viewed as a source of norms for human behavior. The authority of nature has been used to support or condemn various causes.

For centuries, philosophers have insisted that there are no values ​​in nature; this, quite simply, is. Transmuting that "is" into a "must" involves a human act of imposition or projection. Trying to transfer cultural values ​​to nature and appealing to its authority to shore them up is to incur a "naturalistic fallacy" that many authors, throughout history, have tried to banish. However, the temptation persists.

In this work, the author does not intend to make another attempt to end the naturalistic fallacy, but to understand why its predecessors have failed. She argues that the type of species that we are - and not just sensitivity and psychology - influences reason, and she proposes a model of philosophical anthropology based on an inquiry into human reason rather than universal Reason.