Certainty is a powerful idea that has mesmerized philosophers, and especially religious leaders, throughout the ages. Belief in absolute and certain truth has all too often justified the most inhumane behavior toward those not sharing that truth and that belief.
Perfect certainty is one of the dogmas of determinism.
The search for philosophical certainty began with Socrates and Plato. They found that denying some ideas led to logical or mathematical contradictions. Socrates, the first logician, argued that some knowledge followed from the nature of argument itself. He invented the syllogism, literally "with logic or argument."
Plato found geometry, an axiomatic system, to be the perfect model for certain knowledge. Once the axioms and the method of geometric deductions are accepted, knowledge can be demonstrated or proved - Q.E.D.
Aristotle advanced logic to a state that lasted over two thousand years, well into the nineteenth century, when Frege, Peirce, Russell, Gödel, and others found tiny cracks in Aristotle's system of logic. Yet even as he built this great tool of formal reasoning, Aristotle and his students were well aware of its limitations to the realm of ideas.
Contingent facts about the world had no certainty or necessity. Aristotle saw them as involving "accidents." It is logically necessary that if A is B, and if all B are C, then A is also C. It is geometrically necessary that the sum of the angles in a plane triangle equals two right angles.
But it is not necessary that the sky is blue or that the sun will rise tomorrow. Aristotle still felt these things were "caused," but that's another story. That's causality.
Ancient skeptics briefly denied that absolute certain knowledge was possible, but caught themselves when they realized this statement itself seemed too absolute. Thus began a descent into relativism that continues to this day.
Certainty must be disambiguated from its close relatives causality, determinism, necessity, and predictability.
[In Existentialism, the will condemns all the unchosen alternatives to nothingness as it grants being to the one chosen.]