The Qur'an has mentioned both these signs as follows...

The Qur'an has mentioned both these signs as follows: "We shall show to them Our signs upon the horizons (i.e., space) and in their own selves so that it may become manifest to them that He is the Truth." (41:53) This method of knowing God is based on the principle of "cause" and "effect". The signs of nature are the effects of which the ultimate cause is God. Now, let us try to understand the nature and scope of this method more clearly.

NATURE & SCOPE OF THIS METHOD: Whenever we see a beautiful building of great splendour and design, we can easily understand that its architect was an expert in his own craft. Similarly, by looking at a car, an airplane, a computer or any other well-designed product or artifact, we are invariably guided to well-informed and knowledgeable inventors, designers and manufacturers, and we are also made aware of their skill and learning.

In none of these instances is it necessary to actually see the builder, the manufacturer or the designer of such an artifact with our own eyes to testify to his existence. Moreover, when observing all these things, it is not with any of our external senses that we perceive the knowledge and skill of the builders and manufacturers. But, nevertheless, we believe in his expertise and knowledge. Why?

Because the design and order which we perceived in the artifacts forces us to recognize the knowledge of their builders. And from this we reach the conclusion that it is not necessary that something whose existence we wish to believe in should be visible or tangible. There are many things which are not perceptible to our external senses, but we become aware of them through their effects.

For every wise person understands that there can be no effect without a cause, nothing orderly without a wise and knowledgeable designer.

Based on the above, we can divide the things of this world into two categories: Things which are evident to one or more of the five senses; we observe visible things with the eyes, we hear sounds with the ears, we become aware of pleasant and unpleasant smells with our nose, we know bitter and sweet tastes with our tongue, and we feel hot and cold or rough and smooth with the skin of our body.

Things which are not perceived by any of the five senses, but whose existence we can deduce by considering their effects. These facts are not all of one kind, some are material and some are non-material. We shall mention a few of them here.