Yoga Science is one. Just as various specialties in one medical science do not make several medical sciences, so the various specialties within Yoga do not make several yogas. Hatha-yoga, Laya-yoga, Nada-yoga, Mantra-yoga, Kundalini-yoga, and others are only several emphases to harmonize the various levels of human personality in various stages of the practitioner's holistic development. The foundation of all these could be seen within the framework of Raja-yoga, which is Ashtanga-yoga (Yoga of eight limbs) as promulgated by Sage Patanjali.
Of these, Hatha-yoga has become the most popular and practically synonymous with the totality of Yoga, because most individuals identify their self with the body vehicle. However, to make this vehicle the very goal of the journey would be erroneous. This body vehicle is run through the infusion and interaction of subtler forces and essences. The practice of Hatha-yoga is incomplete unless some of these subtler forces and essences such as the mind & prana, are understood, experienced during through practices. And, the moment some of these forces are understood, then the practice of Hatha-yoga unblocks the very channels through which these subtler forces and essences are infused, thus expanding one's awareness. Without this, Hatha-yoga merely becomes another system of physical exercise.
The science of Yoga should remain a method for gaining higher grounds of awareness, without which the exercises themselves would be incomplete and the practitioner would neither gain mastery nor the full benefits of the practice. One of the most authentic text of Hatha-yoga by Svatmarama, the Hathayogapradipika begins thus; "I salute the primeval Lord (Shiva), who taught (Parvati) the Hathayoga-vidya, which is as a stairway for those who wish to attain the lofty Raja-yoga." Just so, the Hathayogapradipika ends with these verses; "Until the prana enters the middle path (of the sushumna stream),until the point (of concentration) becomes firm through the control of prana,until one's vital essence flows naturally and evenly in meditation,Till then all your knowledge (of Hatha) is myth, hypocrisy, and (mere) words." And hence, a careful study of the texts of Hatha-yoga including the one by Svatmarama cannot fail to be impressed by the references to the role the mind and prana plays in the practices, and yet it is rather sad that in present days Hatha-yoga is taught without the subtleties of the practice. It must be understood that the science of Hatha-yoga first appeared as records of physical experiences that occurred naturally to the Yogis when the mind and prana have entered the sushumna stream of Mother Kundalini during the practice of meditation. The yogi's body does habitually and naturally what a beginner in Hatha-yoga is advised to practice as an endeavor. It must be known that even the easiest practices of Hatha-yoga could be elevated to an inner spiritual experience and the subtler essences of the practitioner's personality will suffuse the body with amrita, the immortal energy.