Until the eighth century, and the rise of the Mutazilite theology, Greek philosophy was viewed with suspicion. Despite the political support given to philosophy because of the Mutazilites and the early philosophers, a strong anti-philosophical movement rose through theological schools like the Hanbalites and the Asharites. These groups, particular the latter, gained public and political influence throughout the tenth and eleventh century Islamic world. These appealed to more conservative elements within society, to those who disliked what appeared to be non-Muslim influences. Ibn Rushd, who served a political dynasty that had come into power under a banner of orthodox reform while privately encouraging the study of philosophy, was likely sensitive to the increasing tensions that eventually led to his banishment. Though written before his exile his Decisive Treatise provides an apologetic for those theologians who charged philosophers with unbelief.

Ibn Rushd begins with the contention that Law commands the study of philosophy. Many Quranic verses, such as "Reflect, you have a vision" (59.2) and “they give thought to the creation of heaven and earth” (3:191), command human intellectual reflection upon God and his creation. This is best done by demonstration, drawing inferences from accepted premises, which is what both lawyers and philosophers do. Since, therefore, such obligation exists in religion, then a person who has the capacity of “natural intelligence” and “religious integrity” must begin to study philosophy. If someone else has examined these subjects in the past, the believer should build upon their work, even if they did not share the same religion. For, just as in any subject of study, the creation of knowledge is built successively from one scholar to the next. This does not mean that the ancients' teachings should be accepted uncritically, but if what is found within their teachings is true, then it should not be rejected because of religion. (Ibn Rushd illustrated this point by citing that when a sacrifice is performed with the prescribed instrument, it does not matter if the owner of the instrument shares the same religion as the one performing the sacrifice.)

The philosopher, when following the proper order of education, should not be harmed by his studies, hence it is wrong to forbid the study of philosophy. Any harm that may occur is accidental, like that of the side effects of medicine, or from choking on water when thirsty. If serious harm comes from philosophical study, Ibn Rushd suggests that this is because the student was dominated by their passions, had a bad teacher or suffered some natural deficiency. Ibn Rushd illustrates this by quoting a saying of the Prophet Muhammad, when asked by a man about his brother's diarrhea. The Prophet suggested that the brother should drink honey. When the man returned to say that his brother’s diarrhea had worsened, the Prophet replied, "Allah has said the truth, but your brother's abdomen has told a lie" (Bukhari 7.71.588).

Not all people are able to find truth through philosophy, which is why the Law speaks of three ways for humans to discover truth and interpret scripture: the demonstrative, the dialectical and the rhetorical. These, for Ibn Rushd, divide humanity into philosophers, theologians and the common masses. The simple truth is that Islam is the best of all religions, in that, consistent with the goal of Aristotelian ethics, it produces the most happiness, which is comprised of the knowledge of God. As such, one way is appointed to every person, consistent with their natural disposition, so that they can acquire this truth.

For Ibn Rushd, demonstrative truth cannot conflict with scripture (i.e. Qur'an), since Islam is ultimate truth and the nature of philosophy is the search for truth. If scripture does conflict with demonstrative truth, such conflict must be only apparent. If philosophy and scripture disagree on the existence of any particular being, scripture should be interpreted allegorically. Ibn Rushd contends that allegorical interpretation of scripture is common among the lawyers, theologians and the philosophers, and has been long accepted by all Muslims; Muslims only disagree on the extent and propriety of its use. God has given various meanings and interpretations, both apparent and hidden, to numerous scriptures so as to inspire study and to suit diverse intelligences. The early Muslim community, according to Ibn Rushd, affirmed that scripture had both an apparent meaning and an inner meaning. If the Muslim community has come to a consensus regarding the meaning of any particular passage, whether allegorical or apparent, no one can contradict that interpretation. If there is no consensus about a particular passage, then its meaning is free for interpretation. The problem is that, with the international diversity and long history of Islam, it is all but impossible to establish a consensus on most verses. For no one can be sure to have gathered all the opinions of all scholars from all times. With this in mind, according to Ibn Rushd, scholars like al-Ghazzali should not charge philosophers with unbelief over their doctrines of the eternity of the universe, the denial of God's knowledge of particulars, or denial of bodily resurrection. Since the early Muslims accepted the existence of apparent and allegorical meanings of texts, and since there is no consensus on these doctrines, such a charge can only be tentative. Philosophers have been divinely endowed with unique methods of learning, acquiring their beliefs through demonstrative arguments and securing them with allegorical interpretation.

Therefore, the theologians and philosophers are not so greatly different, that either should label the other as irreligious. And, like the philosophers, the theologians interpret certain texts allegorically, and such interpretations should not be infallible. For instance, he contends that even the apparent meaning of scripture fails to support the theologian's doctrine of creation ex nihilo. He highlights texts like 11:7, 41:11 and 65:48, which imply that objects such as a throne, water and smoke pre-existed the formation of the world and that something will exist after the End of Days.

A teacher, then, must communicate the interpretation of scripture proper for his respective audiences. To the masses, Ibn Rushd cautions, a teacher must teach the apparent meaning of all texts. Higher categories of interpretations should only be taught to those who are qualified through education. To teach the masses a dialectical or demonstrative interpretation, as Ibn Rushd contends Ghazzali did in his Incoherence, is to hurt the faith of the believers. The same applies to teaching a theologian philosophical interpretations.