One of two approaches to yoga outlined in Chapter 2 of Patanjali’s Yoga Sutra. Patanjali was an Indian yoga teacher, believed to live about eighteen hundred years ago. His yoga sutra is considered by most yoga students to be the principle work on yoga availble to us today.
A sutra – which translates as thread – contains a number of aphorisms.
Aphorisms are short statements, shorthand if you like, for a fuller explanation that can be found in commentaries or which may be taught by your own teacher.
Patanjali is a master of the art of aphorism and he packs an incredible amount of knowledge into eahc of his aphorisms. Additionally, each can have more than one meaning and helps create a multi-faceted image in the mind of the reader.
Astanga means ‘eight-limbed’ so, when Patanjali talks about Astanga Yoga, he's speaking about a form of yoga composed of eight interrelated parts. The Astanga yoga that can be found in classes today, isn't the same thing. It's a kind of cut-down version limited mostly to physical exercises.
Patanjali talks about eight limbs because he wants to create an image in our mind of yoga as a living thing, just like you and me. He also means (because yoga is for people and people normally have four limbs) that this living thing has an outer and inner body, each with four limbs.
From this image, we can see that we’re dealing with something that will affect not just our outer being but our inner being as well. Put in another way, Astanga yoga is for body AND mind with each being a part of one whole being.
The four outer limbs are Yama, Niyama, Asana and Pranayama. They can be practised directly; you can do asana; you can do pranayama.
The four inner limbs are Pratyahara, Dyhana, Dharana and Samadhi. They can’t be practised directly. You can’t do Dhyana without some involvement from the outer limbs and the other inner limbs as well (or at least not when you begin and not for some time after that).
If you want to work with Astanga Yoga, then you should be working with all of these things. the limbs of this approach are all meant to be used - meant to be worked on - meant to be improved - together This is important because there is a popular style of modern yoga that only has one limb – Asana – and so although it may be very good for you physically, it won’t work on the whole of your being.