The "Catechism" specifies that all sex acts must be both unitive and procreative. They posit, however, that physical stimulation alone is not sufficient to generate transcendental unitive experiences. In the Unitive stage he experiences a vehement love from his contemplation of the divine. "Casti connubii" explains the secondary, unitive, purpose of intercourse. This iridescence never resolves itself completely into a unitive point of view. A form of prayer corresponding perhaps to the illuminative and unitive ways is called Hesychasm. One can learn to see in this Unitive way almost at will.