We use the light-front “machinery” to study the behavior of a relativistic free particle and obtain the quantum commutation relations from the classical Poisson brackets. We argue that their usual projection onto the light-front coordinates from the covariant commutation relations show that there is an inconsistency in the expected correlation between canonically conjugate variables “time” x + and “energy” p – . This incompatibility between canonical conjugate variables in the light front is discussed in the context of Poisson brackets and a suggestion is made on how to avoid it. PACS Nos.: 12.39.Ki, 14.40.Cs, 13.40.Gp