Dirac on gauges and constraints

This paper examines the relevance to current reflections on the meaning of physical symmetries of Dirac’s view on the use of transformation theory and invariants: that is, the view that the application of transformation theory and the related use of invariants in theoretical physics is closely connected with the inevitable introduction of 'irrelevancies' when attempting a fundamental description of the physical world. In particular, the paper focusses on the relation that can be established between gauges and constraints, on the grounds of Dirac's theory of constrained systems, as presented in his famous 1964 Lectures on Quantum Mechanics.