'ignorance,' nescience, unknowing; synonymous with delusion (moha, s. mūla), is the primary root of all evil and suffering in the world, veiling man's mental eyes and preventing him from seeing the true nature of things. It is the delusion tricking beings by making life appear to them as permanent, happy, substantial and beautiful and preventing them from seeing that everything in reality is impermanent, liable to suffering, void of 'I' and 'mine', and basically impure (s. vipallāsa). Ignorance is defined as 'not knowing the four truths, namely, suffering, its origin, its cessation, and the way to its cessation' (S. XII, 4).

As ignorance is the foundation of all life-affirming actions, of all evil and suffering, therefore it stands first in the formula of Dependent Origination (paticca-samuppāda). But for that reason, says Vis.M. (XVII, 36f) ignorance should not be regarded as "the causeless root-cause of the world ... It is not causeless. For a cause of it is stated thus 'With the arising of fermentations (Āsava) there is the arising of ignorance' (M. 9). But there is a figurative way in which it can be treated as a root-cause; namely, when it is made to serve as a starting point in an exposition of the Round of Existence ... As it is said: 'No first beginning of ignorance can be perceived, Bhikkhus, before which ignorance was not, and after which it came to be. But it can be perceived that ignorance has its specific condition (idappaccaya)" (A.X.61). The same statement is made (A.X.62) about the craving for existence (bhava-tanhā; s. tanhā). The latter and ignorance are called "the outstanding causes of kamma that lead to unhappy and happy destinies" (Vis.M. XVII, 38).

As ignorance still exists - though in a very refined way until the attainment of Arahatship or Holiness, it is counted as the last of the 10 fetters (samyojana) which bind beings to the cycle of rebirths. As the first two roots of evil, greed and hate (s. mūla), are on their part rooted in ignorance, consequently all disadvantageous states of mind are inseparably bound up with it. Ignorance (or delusion) is the most obstinate of the three roots of evil.

Ignorance is one of the fermentations (Āsava) and proclivities (anusaya). It is often called a hindrance (nīvarana; e.g. in S.XV.3; A.X.61) but does not appear together with the usual list of five hindrances.