The spin state is a discrete degree of freedom ; quantum state spaces can have continuous degrees of freedom. For example, a particle in one space dimension has one degree of freedom ranging from − − ∞ ∞ to ∞ ∞ . In Dirac notation, the states in this space might be written as | q ⟩ ⟩ or | ψ ψ ⟩ ⟩ .