What do Parts 3 and 4 of the Constitution deal with?

Part III deals with the Fundamental Rights and contains Articles 12 to 35. In this regard, the framers of the Constitution derived inspiration from the Constitution of the USA (that is, the Bill of Rights). Part III is rightly described as the Magna Carta of India.

Part IV deals with the Directive Principles of State Policy and contains Articles 36 to 51. The framers have borrowed this idea from the Irish Constitution of 1937, which had copied it from the Spanish Constitution. 

Further Reading:

• Directive Principles of State Policy (DPSP)
• Fundamental Rights – Articles 12-35