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Shad Darshana – The Six Philosophical Systems of Hinduism
YogaLondon on 30 September, 2010 | 
From the foundations of the Ancient Vedic Texts grew the development of six orthodox schools of Hindu philosophy. In contrast to the epic tales (Ramayana and Mahabharata) which appealed to the masses, these philosophical systems greatly appealed to the scholars and intellectuals. These six philosophical schools are usually grouped into three pairs:
Nyaya & Vaisheshika
These first two philosophical schools form a theory of the universe:
1) Gautama's Nyaya: A system of reasoning and logic.
2) Kanada's Vaisheshika: The exploration of the significance of time, space, matter, mind and soul.
Purva Mimamsa & Vedanta-Sutra
These two philosophical schools (which eventually merged into one) are the most closely linked to the original Vedic texts.
5) Jaimini's Purva Mimamsa: A work defending and attempting to re-explain the original Vedas
6) Badarayana's Vedanta-Sutra: The true Vedas End (Vedanta), based (amongst other texts) on the Bhagavad Gita.
Samkhya & Classical Yoga
These two schools are often referred to as Samkhya-Yoga. Yoga theory borrows extensively from Samkhya philosophy. This is the branch from which most modern day yoga stems.
3) Kapila's Samkhya: It offers the 25 basic principles (Tattwas) and the Three Gunas.
4) Patanjali’s Classical Yoga: The eightfold path to enlightenment.
All six of the shad darshana offer slightly different philosophies but the same ultimate truth - that everything is ultimately one (Brahman-Atman).
Classical Yoga differs from the other six philosophical schools as it is the only one to offer methods to experience this truth. It is not satisfied by merely offering a theory. It offers instructions for actually achieving higher states of consciousness, which will allow you to experience this Absoluteness yourself. It is for this very reason that Samkhya-Yoga became one of the more popular Indian philosophies. The techniques offered by Classical yoga can be applied in any of the six philosophical schools.
Yoga and God
Although Samkhya and Yoga are commonly grouped as one there are some fundamental differences between the two schools, especially when it comes to the concept of a God and religion.
Samkhya philosophy explains the structure of the universe and the mind, without any reference to a Creator. Instead the universe is said to be in constant creation and destruction through the interaction of purusha (spirit) and prakriti (nature).
Classical Yoga uses the same system of purusha and prakriti but added to this an independent purusha/Supreme Being called Ishvara. It is worth noting that the slightly disjointed way in which the concept of Ishvara is included in Patanjali’s Yoga Sutras has led some scholars to suggest it was a later addition.
Dualist vs. Non-Dualist Approaches
Modern yoga tends to combine Vedanta ideas with Classical Yoga. The Vedanta concept of Brahman-Atman is utilised, in which Brahman is Universal Consciousness and Atman (your spirit/soul) is a part of Brahman. This idea is non-dualist (Advaita), meaning there is no differentiation between a divine Creator and individual Spirit. Brahman pervades everything including you, and all of us can say, "I am Brahman."
In contrast the Samkhya-Yoga texts speak of many Purushas (Individual Spirits/Souls). Add to this the concept of Ishwara (Creator) and you have a dualist (Dvaita) philosophy - A God figure-head as separate from our own Spirit/Soul.
Other Differences between Samkhya and Classical Yoga:
In the dualist Classical yoga, the only way to reach liberation is to drop the body-mind completely. This implies that the only way to become liberated is in death. Other schools of Vedanta argue that liberation in life is possible (Jivamukti).
Samkhya offers the idea of tattwas and from that derive different aspects or levels of the mind, where as Classical yoga simply offers one, Chitta.
Furthermore, Feuerstein in his book, The Yoga Tradition, suggests that Classical yoga seems to be rooted in personal experience, whereas Samkhya seems to be based on theoretical and metaphysical ideas. Patanjali's sutras are a very practical approach to yoga.