Certainty can be defined as either (a) perfect knowledge that has total security from error, or (b) the mental state of being without doubt. Fact: date=May 2008Objectively defined, certainty is total continuity and validity of all foundational inquiry, to the highest degree of precision.Fact: date=May 2008 Something is certain only if no skepticism can occur.Fact: date=May 2008 Philosophy (at least historically) seeks this state. Fact: date=May 2008It is widely held that certainty is a failed historical enterprise.

Emotion

Strictly speaking, certainty is not a property of statements, but a property of people. 'Certainty' is an emotional state, like anger, jealousy, or embarrassment. When someone says "B is certain" they really mean "I am certain that B". The former is often used in everyday language, as it has a rhetorical advantage. It is also sometimes used to convey that a large number of people are certain about B. However the fact that certainty is an emotional state is not always heeded in the literature. The truth is, certainty is an emotional state that is attained by many people every day. In this sense, certainty is linked to 'faith' as a similar state of consciousness or of emotion.

Socrates- ancient Greece

main: Socrates#Knowledge Socrates, often thought to be the first true philosopher, had a higher a criterion for knowledge than others before him. The skeptical problems that he encountered in his philosophy were taken very seriously. As a result, he claimed to know nothing. Socrates often said that his wisdom was limited to an awareness of his own ignorance.

Al-Ghazali- Islamic theologian

main: Al-Ghazali Al-Ghazali was a professor of philosophy in the 11th century. His book titled The Incoherence of the Philosophers marks a major turn in Islamic epistemology, as Ghazali effectively discovered philosophical skepticism that would not be commonly seen in the West until René Descartes, George Berkeley and David Hume. He described the necessity of proving the validity of reason- independently from reason. He attempted this and failed. The doubt that he introduced to his foundation of knowledge could not be reconciled using philosophy. Taking this very seriously, he resigned from his post at the university, and suffered serious psychosomatic illness. It was not until he became a religious sufi that he found a solution to his philosophical problems, which are based on Islamic religion; this encounter with skepticism led Ghazali to embrace a form of theological occasionalism, or the belief that all causal events and interactions are not the product of material conjunctions but rather the immediate and present will of God.