Let us return for a moment to the little fellow with the saw. The word "saw" either means a certain tool which you will find in a carpenter's shop, or it means the past tense of the verb "to see."
This is what had happened to the word during the course of centuries. First of all it had meant only the particular tool which it represented. Then that meaning had been lost and it had become the past participle of a verb. After several hundred years, the Egyptians lost sight of both these meanings and the picture came to stand for a single letter, the letter S. A short sentence will show you what I mean. Here is a modern English sentence as it would have been written in hieroglyphics.