Reason acquired a bad reputation in Islam. This was the result of a tradition which treats refraining from the use of reason in religion as a manifestation of piety. According to this "reasoning," Muslims are expected to refrain from using their reason in matters of religion. Exegetes were expected to suppress their reason on the basis of a hadith according to which the prophet forbade the use of 'reason-based tafsir' as disbelief (kufr). The disparagement of reason has a troubling past in Islam. It was propagated by the Sufis, who perceived people of reason as their enemies and the enemies of Islam. They alleged that there is a "tension" between reason and revelation. The perception that equated reasoning with disbelief goes a long way towards explaining not just the proliferation of violence but the fall of the Islam itself. For a civilization that does not value reason is doomed. It by using reason that we attain knowledge of revelation and receive guidance from it. To this day we hear religious teachers advising their protégés against the perils of reasoning.The rejection of the relationship between causes and effects did a great disservice to Islam. For rejecting the relationship between cause and effect entails a rejection of a significant part of the teaching of revelation. Islam teaches that there is a relationship between the way we act and what we gain from it. If we believe and perform praiseworthy acts, we go to paradise. If we disbelieve and do evil, we go to the fire. Evidence of flawed reasoning is also found in the teaching of the purposes of the sharia. This teaching, attributed to al-Shatibi, fails to highlight justice as a purpose of the sharia. How to explain this glaring omission? For in the Quran, justice is next to piety. In their backlash against the rationalists, who advocated both reason and justice, the traditionists disregarded justice. More evidence of poor reasoning may be found in the elevation of tradition to revelation, the assertion that tradition judges revelation, and the belief in the theory of abrogation. The rejection of reasoning had catastrophic consequences for the Muslim civilization. It facilitated the incorporation of a range of unwarranted assumptions within exegesis and jurisprudence, including the perceptions that revelation is "ambiguous," "deficient," that tradition is revelation, and that revelation is better explained by tradition than reason. Little attention was paid to the fact that the explanation of revelation by tradition also requires the use of reason. Another troubling practice was the subordination of reason to tradition, which was reflected in the belief that tradition had to be followed even against reason. The subordination of revelation to tradition was expressed in the perception that "tradition judges revelation" and that "revelation requires tradition more than tradition requires revelation." Are these statements in agreement with the teaching of tauhid? The subjugation of reason and revelation to tradition tainted the knowledge of Islam. Folklore was engaged to "explain" revelation. What is more, it was expected to do so without the use of reason. This produced a paralysis in the Muslim mind. Contradictory beliefs became embedded in exegesis as well as in jurisprudence. An example is the perception that traditions are "equal" to and subordinate to revelation, simultaneously. Another example is the replacement of parts of revelation by traditions, which resulted from the utilization of the teaching of the abrogation of revelation by tradition. The theory of abrogation enabled extensive tampering with the knowledge of revelation, to the point that it distorted and corrupted its teaching. The alleged abrogation of the peace verses by the ayah as-sayf, taken out of context, transformed the teaching of peace into a political agenda known as Islamism. It transformed Islam as the religion of peace into Islamism as an ideology of war and conquest.