' Hua Hu Ching '

67. To achieve the highest levels of life, one must
continually combine new levels of yin and yang.
In nature, the male energy can be found in such
sources as the sun and the mountains, and the
female in such sources as the earth, the moon, and
the lakes.
Those who study these things, which are only hinted
at here, will benefit immeasurably.

Because higher an higher unions of yin and yang are
necessary for the conception of higher life, some
students may be instructed in the art of dual
cultivation, in which yin and yang are directly
integrated in the tai chi of sexual intercourse.
If the student is not genuinely virtuous and the
instruction not that of a true master, dual
cultivation can have destructive effect.
If genuine virtue and true mastery come together,
however, the practice can bring about a profound
balancing of the student's gross and subtle energies.

The result of this is improved health, harmonized
emotions, the cessation of desires and impulses,
and, at the highest level, the transcendent
integration of the entire energy body.