Need for Philosophy
It  always happens that once the basic necessities of life are satisfied and the  normal struggles of living are won over the human being starts wondering what  the purpose and meaning of life is? The result of such an enquiry is  philosophy.

The  Indian mystics found the answers to all such questions by undertaking their  search within oneself rather than outside. They went to the extent of  experiencing such results of their enquiry which gave them an intuitive capability  to acquire a clearer and deeper understanding of the meaning and goal of human  life. It is because of this special perception their thoughts are called darshana which actually means vision or  realization of the Self. These illuminating thoughts of the seers came to be popularly known as  systems of Indian philosophy.

All the  darshanas or systems of philosophy discovered that in spite of all the best  efforts put in by man; his life is full more of misery than bliss. Hence  finding out the means to escape from the clutches of grief and despair of human  existence, once and for all, became the main goal of their endeavors.

Darshanas and Upanishads
In  relation to the systems of Indian philosophy, the Upanishads played a vital  role.  It is from the Upanishads that the founders of the systems drew  their inspiration.  Their experiences represented a large store house of  philosophic thought in India  from which each thinker propounded certain principles as revealed to him.

Though  philosophy in India  developed from the common reservoir of Upanishadic ideas, it neither stifled  any freedom of thought nor did it stunt its growth. Each philosopher tried to  develop his own conclusions and offered his own reasons in support of them.

SHAD-DARSHANAS OR  SIX SYSTEMS        
According  to the traditional principles of classification, these enlightened philosophic  thought flows of the sages are classified into two broad categories viz.  orthodox (astika) and heterodox (nastika). These words normally convey a  division of thinkers into ‘theist’ and ‘atheist’. 

Orthodox  systems are those which accept the authority of the Vedas, while the heterodox  systems are those which reject it.  To the latter group belong the three  systems of Charvaka, Buddhism and Jainism.

The  ‘Shaddarshanas’, or the six systems of Indian  philosophy belong to the former group.   These systems are called
  1. Nyaya.
  2. Vaisesika.
  3. Samkhya.  
  4. Yoga.  
  5. Purva Mimamsa
  6. Uttara Mimamsa or Vedanta.

They  generally deal with four topics:
  1. Existence and nature of Brahman 
  2. Nature of the jiva or the individual soul
  3. Creation of the jagat or the world.
  4. Moksha or liberation and the disciplines that lead to it.