There are two divisions of the assent: certainty (yaqīn) and probability (žann). The assent assumes a preponderance of belief about whether or not the statement is true or not, whether or not there is only a chance (iĥtimāl) that it may be true or not, or whether there is a certain determination as to whether the proposition is true. If the possibility of the predicate being false is completely denied, then we call this certainty. But if there is a weak possibility of the predicate not being true, then we call this probability.
We will elaborate on the situation further. If you are presented with a certain predicative proposition, then you will react to this in four possible ways. You may decide that this proposition can only be true or only be false, or you may accept that the possibility that it could be true or could be false. The first is certainty. The second case, however, can take three possible forms. Either the proposition could be equally true or equally false, or there could be a higher probability of it being true or a higher probability of it being false. If they are equal, we call this doubt (shakk). If there is a preponderance of belief [but not certainty] regarding the truth of the statement, we call this probability [žann]. If there is a preponderance of belief about it being false, we call this estimation (wahm).2 Estimation is one of the categories of ignorance (jahl), and it is the opposite of probability. These, then, are the four possible situations (and there is no fifth possibility):
1) Certainty (yaqīn). This is a complete assent of whatever is the import of the predicative proposition, without any possibility of it being false; or there is a complete assent of that proposition‟s falseness. This is the highest form of the assent.
2) Probability (žann). This is the likelihood of the predicative proposition being true. This is the lowest form of the assent.
3) Estimation (wahm). This where one holds some possibility for the statement being true, but his belief falls on the side of its negation.
4) Doubt (shakk).This is where the likelihood of the predicate‟s truth or falsehood is considered equal.
An admonition: You should understand two things from what has been said. The first is that estimation and doubt are not kinds of assent; in actuality, they are kinds of ignorance. The second is the probability and estimation always stand in a reciprocal relationship: if you have an estimation about the soundness of a given propositional statement, this means that you have a probabilistic belief (žann) about it being false. And if you have an estimation about the statement being false, then you have a belief about it being true. As such, the probabilistic belief about one possibility [of the statement being true or false] is an estimative belief about the other possibility.