In general, man can attain ontological (takwīnī) and legislative (tashri‘ī) knowledge through the following four ways:
- Sensual way (ṭarīq-e ḥissī) or sensual knowledge: sensual knowledge has the following characteristics:
Firstly, it is particular and personal.
Secondly, it is confined to material realities.
Thirdly, it is limited to the outward aspects of material phenomena and it has no access to the quiddities of things.
Therefore, although it has an important contribution in worldview and man is not independent from it, sensual knowledge cannot provide a comprehensive and firm worldview for man.
- Rational way (ṭarīq-e ‘aqlī): the components of this type of knowledge are universal rational principles and rules and its form consists of rational analysis and synthesis. This knowledge has the following characteristics:
a. It is universal and all-encompassing.
b. Its scope is the absolute existence including both the material (māddī) and the immaterial (mujarrad).
c. It encompasses even the essence and quiddities of things, yet it is incapable of discerning and knowing the manifestations and particularities of things.
In view of the above points, we can conclude that since some manifestations and particularities are outside the domain of the sensual and rational knowledge, it follows that the sensual and rational knowledge cannot separately or jointly address the epistemological need of man, although they have a big share in this regard and without them, the epistemological system of man cannot take shape.
- Way of inward overture and intuition (ṭarīq-e kashf wa shuhūd-e bāṭinī) this type of knowledge is intuitive (shuhūdī) and presential (ḥuḍūrī); that is, through his heart and soul, man directly witnesses the truths within and outside his being.
Intuitive witnessing and discernment of external truths can be realized provided that the self (nafs) is purified through abstinence (riyāḍah) and free from the entanglements and fetters of materialistic inclinations. Abstinence necessitates rational and lawful regulations. For this reason, this method is in need of reason (‘aql) and the Divine law (sharī‘ah)
- Way of the Divine revelation and inspiration (ṭarīq-e waḥyi wa ilhām): although this type of knowledge is based upon sensory perception (ḥiss) and reason, Divine revelation deepens man’s sensual and rational knowledge because Divine revelation unveils truths which are beyond the realm of man’s sensual and rational knowledge; for example, knowledge of the details of laws and morality (the branches of religion or furū‘ al-dīn) as well as issues pertaining to the high levels of discursive knowledge about God such as the Divine Unity (tawḥīd) or subjects related to the next world.