  We provide a new formulation of the Pais-Uhlenbeck oscillator which is a
prototype of a higher derivative model. Different parametrisations that reveal
the model as a combination of two simple harmonic oscillators are introduced.
Conventional results are reproduced in one realisation. In another, all
problems related to lack of unitarity or boundedness of energy are eliminated
since the hamiltonian is expressed as a sum of the hamiltonians of two
decoupled harmonic oscillators. Recourse to imaginary scaling transformation or
PT-symmetry, as advocated in the literature, are totally avoided.
