It is through reason that man justifies his faith. Rational justification strengthens his convictions. Rational argument is thus an intellectual need of every believer. Without this he would not be able to stand firmly by his faith. It is reason which transforms blind faith into a matter of intellectual choice.

History shows that man has employed four kinds of argument to find rational grounds for his faith. Each of these reflects different stages in his intellectual development.

Natural Argument
The first kind of argument is one based on nature. That is, on simple facts or common experiences. This has been the most commonly used since ancient times. Some examples of this kind are found in the Quran, one of which relates to the Prophet Abraham. It is stated as follows in the Quran:

Have you not considered him (Namrud) who disputed with Abraham about his Lord, because God had given him the kingdom? When Abraham said: ‘My Lord is He who gives life and causes to die,’ he said: ‘I too give life and cause death.’ Abraham said: ‘So surely God causes the sun to rise from the east, then you make it rise from the west.’ Thus he who disbelieved was confounded; and God does not give guidance to unjust people. (2:258)

We find another example of the argument based on natural reasoning in the Quran:

Thus did We show Abraham the kingdom of the heavens and the earth, so that he might become a firm believer. When night overshadowed him, he saw a star. He said: ‘This is my Lord’. But when it set, he said: ‘I love not those that set.’ Then when he saw the moon rising, he said: ‘This is my Lord.’ But when it set, he said: ‘Unless my Lord guide me, I shall surely be among those who go astray’. Then when he saw the sun rising, he said: ‘This is my Lord. This is the greatest.’ But when it set, he said: ‘O my people! Surely, I am done with what you associate with God.’ (6:75-78)

Argument of this kind may appear to be simple, but they are invested with deeper meaning. For this reason, they have been engaged in as much in the past as today.

Philosophical Argument
The second kind of argument is that first propounded by Greek philosophers. Based on pure logic, it was so popular in the medieval ages that Jews and Christians and Muslims all incorporated it into their theological system. Commonly known as First Cause, it may be summed up as follows:

The world man observes with his senses must have been brought into being by God as the First Cause. Philosophers have argued that the observable order of causation is not self-explanatory. It can only be accounted for by the existence of a First Cause. This First Cause, however, must not be considered simply as the first in a series of successive causes, but rather as the First Cause in the sense of being the cause for the whole series of observable causes.