In Islamic philosophy four definitions have been represented about self evidence and speculative knowledge which its common definition is "required to think and not required to anything of think".Explaining conceptual and extensional relationships of self evidence with concepts such as clarity or certainty would help us not to mistake and not to mix different aspects of epistemology together and so, protect ourselves from epistemic mistakes.In this article, self evidence has been compared with clarity & certainty from the conceptual perspective. It has been concluded that the common definition of self-evidence from the point of conceptualization has nothing to do with certainty & clarity, although this conclusion cannot be said about other uncommon definitions.Also, among the self-justified proposition, only the vejdanyyat propositions require these concepts and only the apriori & vejdanyyat & estimative propositions require the certainty and the others don't have any relation with these concepts.

The present article consists of two main sections. In the first section the writer tries to deal with. the topics which in contemporary epistemology has been advanced about tradional foundationalism, anq in the meantime to show both the weaknesses and strengths of these theories briefly. Following this preliminary discussion, in the second section besides the review of Ibn Sina's point of view about the problem of foundation and principles of knowledge, it has been shown that this theory can be included in the foundationalist theories but with a special reading. This theory, with its characteristic features (including, its being foundation of higher beings in relation to lower beings in all kinds of knowledge from observation to certainty, foundational mode of concept for assertion, foundational mode of axioms of every science for the problems of that science, foundational mode of higher sciences in relation to lower sciences and also foundational mode of immediate perceptions for other kinds of knowledge and at the top of immediate perceptions foundational mode of basic self - evident propositions both potentially and, complementary for all kinds of indirect knowledge) neither follows the present-day traditional foundationalism that we deal with in the first section nor is susceptible to the many difficullies of traditional foundationalism of today.

The present paper deals with the theory of Ibn Sina's certain judgmental knowledge in terms of determining its constituent parts. Given Ibn Sina's existing ideas, these constitutive elements include belief, bi-dimensionality of belief, stability, and existence of middle term (in non-axioms). Nevertheless, regarding the notion of truth, we should say that Ibn Sina's considering it a constituent part creates several problems. The writer believes that since this point has not been directly stated in Ibn Sina's views, truth is necessary for a specific type of certain affirmative knowledge. Truth is neither a constituent of certain judgmental knowledge nor something external to it, rather, it is necessary for it.

Foundationalism is considered the most important approaches in epistemology. Traditional foundationalism is expounded in present article. Its main claim is the division of beliefs into two kinds: Basic beliefs and deductive beliefs. Because of the regressive argument, all deductive beliefs finally should be referred to basic beliefs.In present essay, meanwhile explaining the objections to foundationalism, I would offer the responses regarding to Tabatabaii’s epistemological system. Fallibility and corrigibility are considered the main deficiency of foundationalism theory.Tabatabaii explains both the possibility and the method of grasping certain knowledge on the basis of three principles. He emphasizes that all deductive beliefs should referred syllogistically to basic particularly self-evident propositions.

“Epistemology of Mahdism” is a conditional or doubling epistemology which analyzes the knowledge resulted from Mahdism with a logical perspective and answers the questions like: Is it possible to have certain knowledge of the terms of Mahdism? What are the ways and sources of knowledge of the terms of Mahdism? Are Messianic terms capable of being true or false? In the terms of being true, what does their truth mean and how we can prove them to be true? The writer believes with the cognitive faculties of sense, reason, heart, acquired and intuitive knowledge, one can achieve the certain knowledge of Messianic issues. The certain knowledge should be acquired either through the evidence in the form of apriority and matters of conscience or via the definite proof. According to the theory of foundationalism, if some of Messianic terms are of the types of actually granted issues, i.e apriority and matters of conscience, they are authorized and do not need to be justified, because their truth is in their essence. Otherwise, Messianic terms are justified based on reasons and arguments. It is undoubtedly true in the terms of Messianism, there are matters of conscience which are actually granted and physical phenomena and transmitted data which are proximately granted.

Recognizing truthfulness of basic self-evident premises is one of the important concerns of epistemology. Ibn-e Sina considers these propositions as self-evident truths (classical theory). Among the contemporary thinkers, Mesbah Yazdi does not consider this solution as sufficient and has found it as problematic. According to his opinion, verification of the truthfulness and the true totality of the propositions are dependent on transcending concepts and using intuition knowledge instead. This is how one can make sure that self-evident premises are not abstract and mental textures, but objective and general truths. The following essay includes 3 parts: first is statement of problem. Second part is the explication and criticism of mesbah′s classic theory. And third part is dealing with resolving questions posed about it. There are two major issues in this sphere: first, both concepts of reference of basic self-evident premises to intuitive knowledge are true. The second issue is that verifying the truthfulness of general proposition over a specific one is due to a mistake concept in respect of significance for it in respect of existence. In conclusion, we think there are some traces of Mesbah′s theory in Avicenna's too.

Analyzing whatness and conditions of knowledge realization includes ancient questions in logic, metaphysics, epistemology and philosophy of science. In Avicennian ideology, the identity of “knowledge” is merely rational and certain knowledge which demands acquisition. Avicenna does not agree with background and innate knowledge and for him, the foundation of the certain knowledge in two fields of apprehension and judgment is originally based upon the most fundamental units of knowledge. He believes that in the process of acquiring certain knowledge, “belief” is the first factor having psychological identity which is changed into an objective certainty within specific conditions and proof is made by a useful reasoning of certain knowledge. In Avicennian thought, experience is the product of rational deduction and sensory induction. A certain and general knowledge would not be achieved from incomplete sensory induction and it has only a preparatory function. However, experience which is different with induction creates certain and general knowledge. In his philosophical works and by using logical principles and argumentative induction method, Avicenna has dealt with proving God as a theoretical and nontrivial issue. Application of Avicenna’s epistemological principles in proof of God appears to be, to some extent, in conflict and the origin of some controversies in this regard that their compatibility is explainable by a general and comprehensive look upon his epistemological system.