Every vowel, such as "a" or "e" or "o," has its psychological significance, and the composition of every word has a chemical and psychological significance. The Yogis have certain words which they repeat in the morning or in the evening for so many times, and from saying those words they derive a certain illumination or come to a certain state of exaltation. It is this very science which was called by the Sufis of ancient times zikr. This means a science of bringing about desirable results by the repetition of the proper words or phrases.