Habeas Corpus ('you have the body'): Compels production of detained person before court to examine legality of detention. Most important writ for personal liberty. Wide scope — lies against State AND private individuals. Available even during Emergency (subject to Art. 359 orders — but Arts. 20/21 cannot be suspended).
Mandamus ('we command'): Issued to public authority commanding performance of a public duty which has been refused or neglected. Enforces statutory duties, constitutional duties. Does NOT lie against: private contractual obligations; purely discretionary decisions (only compels exercise of discretion, not a particular outcome); judicial authority in purely judicial matters; private individuals.
Certiorari ('to be certified'): Issued to inferior tribunal to bring record before superior court for examination and quash if defective. CURATIVE — issued AFTER decision. Grounds: excess of jurisdiction, lack of jurisdiction, violation of NJ, error apparent on the face of record (Syed Yakoob v. K.S. Radhakrishnan, 1964).
Prohibition: Issued to inferior tribunal to STOP it proceeding in excess of jurisdiction. PREVENTIVE — issued BEFORE decision is made. If decision already made, certiorari is the appropriate remedy.
Quo Warranto ('by what authority'): Issued against a person who has usurped or holds a public office without legal authority. Only lies for public offices of a substantive character created by statute or Constitution. A discretionary writ — not a writ of right (University of Mysore v. C.D. Govinda Rao, 1964).