Abstract
Knowledge, despite the fact that there is no a complete definition yet, is one of the main discussion issues of philosophy, theology and tasawwuf. Some claim that knowledge occurs by means of reason that processes data transmitted by sense organs while others claim that knowledge occurs by means of a light released in the heart of humans. Since it is not mutual for all humans to have the light in the heart, focusing on the other way of knowledge, that it is to follow reason, seems more significant and remarkable at this stage. In this respect, we attempt to investigate in this article how to treat reason and rationality in Iḥyā al-ʿulūm al-dīn, the work of Ghazzālī who has a strong impact on the Islamic thought. In this article our purpose is not to draw an exhaustive profile of Ghazzālī but to make an assessment for neutral, positive and negative statements of Ghazzālī with respect to reason and rationality in the work. While explaining his neutral statements it is a requirement to touch on the terms heart (qalb) and knowledge (ʿilm) as well because they are relevant to the subject of reason. The work, Iḥyāwas written by Ghazzālī for those who are responsible to preach to and have a close connection with masses. Since reason is the tool of knowledge only shared by all humanity, studying the ideas, especially ideas on reason and rationality found in this work gains importance.