The founder of the Transcendental Meditation movement, Maharishi Mahesh Yogi, was insistent that the TM mantras came from a long "Holy Tradition,"and that the "purity of the teaching" had to be maintained. He taught that each individual instructed in TM had to have his or her mantra carefully chosen by a highly trained teacher in order for it to be suitable for that individual and to produce the best results. It was implied that choosing the correct mantra involved metaphysical knowledge.
Mahesh cautioned teachers of TM that except during initiation, they were never to say aloud or write down the mantras that he had taught them. They weren't even permitted to say them to other TM teachers. So it wasn't until TM teachers got disillusioned, broke Mahesh's rule, and started sharing mantras that they discovered that Mahesh, rather than passing down the categories for mantras with perfection, precision and purity, had actually taught mantras based on changeable categories.
Readers of TM-Free Blog and other websites skeptical of TM now know that over the years, Mahesh has taught TM teachers to choose the mantras based upon the initiates' age, or sex, or age plus sex. On different TM Teacher Training Courses (TTC), Mahesh added mantras, deleted mantras, changed the spelling or pronunciation of mantras, and changed which category got which mantra.
The excellent website minet.org, written many years ago by TM-Free Blog coordinator Mike Doughney, provides the following table, listing which mantras Mahesh taught on different TTCs: