What is meant by “other authorities” under Article 12 of the Indian Constitution?

The interpretation of the term “other authorities” in Article 12 had caused a good deal of difficulty, and judicial opinion has undergone changes over time. To clarify the status, the Supreme Court has developed the concept of an “instrumentality” of the state. Any body which can be regarded as an “instrumentality” of the state falls under Article 12. The reason for adopting such broad view is that the Constitution should, whenever possible, “be so construed as to apply to arbitrary application of power against individuals by centres of power. The emerging principle appears to be that a public corporation being a creation of the state is subject to the Constitutional limitation as the state itself”.