ABSTRACT
In this chapter we shall present the dilemma between an undulatory
and corpuscular understanding of quantum systems. We shall show
the historical reasons that have led to the necessity to posit the
quantization principle. Then, we shall focus on the concept of
observables and show two crucial aspects of quantum observables:
there are different possible bases to expand a quantum state
(hence superposition is a relative concept) and observables do not
necessarily commute. Finally, the concept of non-local features is
introduced.
