Aristotle refutes Plato's Theory of Ideas on three basic grounds: that the existence of Ideas contradicts itself by denying the possibility of negations; that his illustrations of Ideas are merely empty metaphors; and that they theory uses impermanent abstractions to create examples of perception. Though the theory is meant to establish concrete standards for the knowledge of reality, Aristotle considers it fraught with inconsistencies and believes that the concept of reality depends upon all forms' correlations to other elements. Ideas, Plato believes, are permanent, self-contained absolutes, which answered to each item of exact knowledge attained through human thought. Also, Ideas are in Plato's view concrete standards by which all human endeavor can be judged, for the hierarchy of all ideas leads to the highest absolute - that of Good. In addition, the theory claims that states of being are contingent upon the mingling of various Forms of existence, that knowledge is objective and thus clearly more real, and that only the processes of nature were valid entities. However, Aristotle attacks this theory on the grounds that Plato's arguments are inconclusive either his assertions are not al all cogent. Aristotle says, or his arguments lead to contradictory conclusions. For example, Aristotle claims that Plato's arguments lead one to conclude that entities (such as anything man-made) and negations of concrete ideas could exist - such as "non-good" in opposition to good. This contradicts Plato's own belief that only natural objects could serve as standards of knowledge. Also, Aristotle refutes Plato's belief that Ideas are perfect entities unto themselves, independent of subjective human experience. Ideas, Aristotle claims, are not abstractions on a proverbial pedestal but mere duplicates of things witnessed in ordinary daily life. The Ideas of things, he says, are not inherent to the objects in particular but created separately and placed apart from the objects themselves.