There is room for asking the proponent for reasons in favor...

There is room for asking the proponent for reasons in favor of his own existence and that of other people which will oblige him to accept some self-evident propositions. Then, on the basis of the self-evident propositions, some other theoretical points may also be proven.

The denial of the being of material existents, as is understood from the words of Berkeley, for he considered being an existent equivalent with being a perceiver or something perceived, and perceivers include God and non-material existents. So, it is decided that perceived things are to be limited to perceptible forms (essentially known ( ma‘lūmāt bil-dhāt )) which are realized within the perceiver himself, not outside him.

In this way there is no room for the objective existence of material things. Other idealists, like Hegel, may be joined to those mentioned above, for they imagine the world to have the form of thoughts for absolute spirit, which are considered to be subject to the laws of logic (but not of cause and effect).

There is room to include along with the idealists, who deny a part of reality, that is, material reality, the materialists, who are also deniers of reality, and they truly deny the greater part of reality. Moreover, the idealists are more logical than the materialists, for their position rests on knowledge by presence and internal experience which have absolute value, however much their inferences may be erroneous.

However, the position of the materialists rests on that which is given by the senses, which is the source of most perceptual errors. By attending to the various types of denial of reality, we reach the conclusion that only the first hypothesis implies an absolute denial of reality, and each of the other hypotheses implies merely a denial of a part of reality and a limitation of its circle.

On the other hand, for each of the five kinds of hypothesis, there is another hypothesis which appears in the form of doubt in absolute reality or with respect to specific realities. If these doubts are mingled with a denial of the possibility of knowledge, that is, if in addition to presenting his own doubt he claims that logically no one can have knowledge, this sort of claim is related to epistemology, and the answer to it is given in its own place.

However, if the presentation of doubt is not mingled with a denial of the possibility of knowledge, the answer to it may be found in ontology.