When is the oath taken by a Minister (in)valid?

News:During the oath-taking ceremony of the Maharashtra government,the Chief Minister with other ministers altered the oath by invoking the names other than mentioned in the Constitution.

Facts:

Constitutional provisions related to Oath:

Article 164(3): 

• It states that before a Minister enters upon his office, the Governor shall administer to him the oaths of office and of secrecy according to the forms set out in the Third Schedule.
• Article 164 also makes it clear that the text of the oath is sacrosanct and the person taking the oath has to read it out exactly as it is, in the given format.

Third Schedule: 

• It requires the taker of the oath to either swear in the name of God or to solemnly affirm to bear true faith and allegiance to the Constitution.

Role of the Governor: 

• Once Governor takes it as read and the Secretary to the Governor has attested that the oath has been administered,it cannot be legally challenged.
• However,if the person deviates from the text,it is the responsibility of the Governor to interrupt and ask the person being sworn in to read it out correctly.

Examples of Deviation in Oath:

• In 1990, the oath by Devi Lal as deputy prime minister was challenged in the Supreme Court as being unconstitutional as the Constitution provides only for the Prime Minister and ministers. 
• However,the Supreme Court upheld the oath as valid and stated that describing a person as Deputy Prime Minister is descriptive only and such description does not confer on him any powers of Prime Minister.
• It also ruled that the description of a minister as Deputy Prime Minister or any other type of ministers such as minister of state or deputy minister of which there is no mention in the Constitution does not vitiate the oath taken by him so long as the substantive part of the oath is correct.