यमनियमासनप्राणायामप्रत्याहारधारणाध्यानसमाधयोऽष्टावङ्गानि॥२९॥
yama = abstinence; niyama = observance; asana = posture; praaNaayaama = breath control; pratyaahaara = sense withdrawal; dhaaraNaa = concentration; dhyaana = meditation; samaadhayaH = contemplation, absorption or superconscious state; aShtau = eight a~ggaani = limbs or parts
Sw. Satchidananda
The eight limbs are listed as above.
Bryant
"The eight limbs are abstentions, observances, posture, breath control, disengagements of the senses, concentration, meditation, and absorption."
In sutra 1.12 practice (abhyasa) and dispassion (vairagya) were mentioned as a means to samadhi. In sutra 2.1, tapas, swadhyaya and Ishwara-pranidhana were given as means to diminish kleshas and help attain samadhi. Here Patanjali, in the subsequent sutras, provided the eight limbs of yoga as the means to attain the goal of yoga. It is important to perform all the eight limbs successfully to attain the objective of yoga.
They are called LIMBS, in order to make clear that they are aspects of one holistic system, called LIFE. This further implies that they canb and should be cultivated SIMUTANEOUSLY. The are not to be considered as STAGES of development, but as aspect that improve simultaneously, as our Consciousness rises.