Explanation of the author's (may Allah have mercy on him) statement: "… And as for the yaa: it is the sign of the accusative case in the dual and the plural …"

The Shaykh :"And as for the yaa: it is the sign of the accusative case in the dual and the plural" Before we move on to the sound feminine plural, which is in the accusative case with a kasrah, what is the sign of its nominative case? The dhammah. Okay, correct. The yaa is the sign of the accusative case in the dual and the plural. We have already discussed the meaning of the dual, haven't we? It indicates two by an addition that suffices for two coordinated elements that agree in form and meaning, right? So, the dual is in the nominative case with an alif and in the accusative case with a yaa. The sound masculine plural indicates more than two, provided the singular form is sound in its construction. If you wish, you can say it is the plural formed with an added waw and noon. The sound masculine plural… the dual and the plural. The plural here is the sound masculine plural. What is the sign of its nominative case?
The student: With a waw.

The Shaykh : With a waw, and in the accusative case
The student: With the yaa

The Shaykh : with a yaa. You say: "I saw." In the dual, you say: "I saw the two men." It is not correct to say: "I saw the two men" (using the nominative form). And in the plural, you say: "I saw the Muslims." It is not correct to say: "I saw the Muslims" (using the nominative form), because when it is in the accusative case, it must be with a yaa. And Allah knows best.