In this paper the philosophical foundations of the first Portuguese Constitution are submitted to critical analysis. Drafted in the aftermath of the 1820 Revolution, the Constitution of 1822 is deeply determined by contradictory tensions and forces. We may see in it the trace of the freedom trends developed in the Enlightenment period and led to practical terms in the dramatic battleground of the French Revolution. Nevertheless, the Portuguese Constitution of 1822 reflect also the energetic resistance from the conservative sectors and values of the Portuguese society and also the coming influence of the Restoration Age political philosophy, aimed to fight the rationalistic paradigm of natural right constitutional theories.