Without words there can be no speech, without letters, no words. We begin to study a language by learning the alphabet. Each alphabet contains two kinds of letters, vowels and consonants. Without either of these human speech would just go to pieces. 

   There is a scientific fiction novel in which the inhabitants of an unknown planet speak to each other by means of sounds consisting only of consonants. But that is pure science fiction!

   Nature speaks to us in the language of chemical compounds. And each of these is a sort of combination of chemical "letters," or elements occurring on Earth.

   The number of such "words" exceeds three million. But there are only just over a hundred "letters" in the chemical "alphabet."

---