Introduction
Article 20 of the Indian Constitution protects Indian citizens from arbitrary and unfair treatment by the state. This article is part of a fundamental right and guarantees individuals certain guarantees against conviction and punishment for crimes.

The principles enshrined in article 20 are critical to ensuring the rule of law and protecting individual rights in a democratic society. It is also important to prevent abuse of power by the state and maintain a balance between individual freedom and the interests of society as a whole.

Clauses under Article 20

Article 20 provides protection in respect of conviction for offences. Following are the three clauses under Article 20:

(1) No person shall be convicted of any offence except for violation of the law in force at the time of the commission of the act charged as an offence, nor be subjected to a penalty greater than that which might have been inflicted under the law in force at the time of the commission of the offence.

Article 20(1) of the Constitution of India provides that no person shall be convicted of any offense unless the act charged as such is in violation of the law in force at the time the act committed. This means that you cannot be convicted of an act that did not constitute a criminal offense at the time you committed it.

This provision is known as the doctrine of ex post facto law. This is an important safeguard against arbitrary and retrospective application of criminal law. Article 20 is not absolute and is subject to reasonable limitations. For example, Article 20(1) does not prevent the legislature from enacting legislation retrospectively if it is in the public interest or serves another reasonable purpose.

(2) No person shall be prosecuted and punished for the same offence more than once.

Article 20(2) of the Indian Constitution provides protection against double jeopardy. The law provides that no person may be prosecuted and punished for the same crime more than once. This provision ensures that a person cannot be tried and punished twice for the same crime. However, if different crimes are committed based on the same act, each crime may be charged and punished separately

(3)No person accused of any offence shall be compelled to be a witness against himself.

Article 20(3) of the Indian Constitution provides protection against self-incrimination. It provides that no person suspected of a crime may be forced to testify against him. This means that a person cannot be forced to testify against him. This provision is based on the principle that it is the duty of the prosecution to prove the guilt of the accused, but not the duty of the prosecution to prove the accused's innocence.

Article 20(3) does not prevent the State from forcing individuals to testify in certain circumstances, such as when a public official is under investigation for corruption or when public safety is at risk.

Landmark Cases under Article 20
Kedar Nath Singh v. State of Bihar: In this case, the Supreme Court ruled that Article 20(1) applies only to substantive criminal law and not to procedural law. The court also ruled that the doctrine of ex post facto law applies only to criminal law and not to civil law.
State of Bombay v. Kathi Kalu Oghad: In this case, the Supreme Court ruled that Article 20(2) applies not only to subsequent prosecutions but also to subsequent judgments. The court also ruled that protection from double jeopardy applies only to those who have been tried and acquitted of the same crime, or who have been convicted and punished.

Nandini Satpathy v. P.L. Dani: In this case, the Supreme Court ruled that protection against self-incrimination is not absolute and can be waived by the defendant. The court also ruled that one cannot be forced to testify against himself, but that he could give such testimony voluntarily.

Mithu v. State of Punjab: The Supreme Court of India has interpreted Article 20 in various cases to broaden and clarify its scope. In this case, the court held that double jeopardy protection applies even if a person is convicted in a lower court and subsequently acquitted in a higher court.

Selvi v. State of Karnataka: In this very important case, the Apex Court enunciated that the protection against self-incrimination also applies to narcoanalysis, brain mapping, and lie detector tests.

Conclusion
Article 20 of the Indian Constitution provides important safeguards for Indian citizens against arbitrary and unfair treatment by the state. This means you can't be convicted of an act that didn't constitute a crime at the time you committed it, you can't be tried and punished twice for the same crime, and you can't be forced to testify against yourself. It is guaranteed that you cannot be prosecuted contrary to the rights enshrined. These safeguards are important to protect the fundamental rights and freedoms of individuals in India.