There is no need for any other thing to make its notion clearer...

There is no need for any other thing to make its notion clearer; because a defining term must always be immediately known and clearer than the defined term. But nothing is more evident than existence. All defining terms of existence are but explanations of the word; they can neither be a "definition" nor a "description." Since existence is absolutely simple as will be explained -, it has no specific difference or genus, and hence has no definition.

It can not have any description, because a "description" is obtainable only by an accidental property which is part of the five universals whose division itself is based on the thing-ness of quiddity, while existence and its properties are derived from an entirely different source2. The deepest reality of existence has in the extremity of hiddenness3.

Because its deepest reality is external, if its reality were to come to our mind as one thing among others this would loose its reality, because the reality in so far as it is reality -in contrast to its notion- must be external and remain outside the mind.

Furthermore, if its reality such as fire were the actualized in the mind in contrast to its effects would also be actualized - and in our example our mind would be burnt by the fire!Mulla Sadra says4: "The truth of existence is the clearest thing in appearance and presence; and its essence is the most hidden thing in grasping and understanding the depth of its reality" In another book, entitled "On the explanation of grasping the truth of existence" he says5: "It is not possible to conceive the reality of existence and its depth of truth, neither by a definition that consists of genus and differentia nor by a definition that consists of genus and special accident nor by a meaning equal to existence.

Because, the conception of the truth of external truth of every thing is acquisition of that thing in the mind and the transition of that meaning from the external to the mind. This action is obtainable about every thing other than existence (i.e. quiddities), but it is not possible about existence (because the transition of existence from the external to the mind, would annul its truth, and what is grasped from of by the mind is a phantom of the truth of existence not its reality).