We should know that concept such as necessity and non-necessity...

We should know that concept such as necessity and non-necessity, or necessary and unnecessary are evident and certainly need no definition for their presence in the mind, and even such concepts cannot be defined. These concepts are gradually and automatically are formed in the human mind. Therefore, we do not intend here to define these concepts, and have only tried to show to which concepts of the mind the philosophers refer by the terms ‘necessity’ and ‘non-necessity’.

Necessity and impossibility The above-mentioned necessity and nonnecessity were not specific to any special attribute. In general, the relationship f each attribute with the thing it describes is either necessary or unnecessary, that is, it is either an attribute inseparable from that thing, or it is a separable attribute. ‘Even’, for example, is the necessary attribute of number eight, whereas whiteness is the unnecessary attribute of the flower.

Now we turn our attention to existence and non-existence. As the relationship of one thing and its attributes could be either necessary or unnecessary, the existence or nonexistence of one object could be necessary or unnecessary. In other words, the existence of one things can be necessary or unnecessary, and its non-existence can also be necessary or unnecessary.

In technical terms, things that have a necessary existence are called ‘necessary’, and those whose non-existence is necessary are named ‘impossible’. The necessity of existence is also named ‘necessity’, and the necessity of nonexistence is called ‘impossibility’. So, when we say something is necessary, we mean its existence is necessary, it must exist, and its non-existence is impossible.

On the other hand, when we say something is impossible, we mean its non-existence is necessary, it should not exist, and its existence would be impossible. For further clarification of the issue, let’s consider one of the phenomena, the storm, for example. Suppose that we know all the factors responsible for the existence of the storm, and decisively judge that the storm must exist.

In other words, with this supposition the storm will necessarily exist, and, in philosophical terms, it is necessary. Now, suppose that some or all of these factors do not exist; then, according to the judgment of the intellect, the storm should not exist. In other words, with this supposition the storm would be necessarily non-existent, and in philosophical terms it would be impossible.