本文主旨在於探討並拒斥在1980 年代一群認知科學家依其研究結果而主張的「蒼涼蘊涵」：人類是不理性的。本文首先解析這些認知科學家建立此結論時所依據的前提，再逐一反駁。另一方面，Stich 檢討了文獻上訴諸天擇演化以辯護人類理性的主張，並重新建構了「天擇論證」，然後提出三件反駁。本文檢視Stich 這三件反駁，並藉由指出其思考不足之處，來修改天擇演化論證，以試圖說明理性與心理推想系統之間的關聯，並重新開啟以演化理論辯護人類理性之路。

This essay is to reject the so-called “bleak implication”—human beingsare irrational in nature, which was said to follow from experiments on human reasoning in the eighties. The rejection is advocated by way of re-constructing for the cognitive scientists their argument for the bleak implication. Meanwhile,Stich constructs what he calls the “Selection argument” for human rationality,and then rejects it. This essay examines his arguments and argues that his objections are defective. This essay then revises the selection argument to show how human rationality is connected to the design and performance of human reasoning mechanism with the hope that we may re-open the possibility of defending human rationality from an evolutionary point of view