Today we have to learn to differentiate and distinguish, without the need of separation. In this sense, there are two pairs of concepts clearly differentiable and not necessarily separable: by one side, complexity and complex thought, and by the other side, disciplinary knowledge (multi-poli and inter-disciplinary) and transdisciplinary knowledge. For classic science, complex thought and
... [Show full abstract] trans-disciplinary knowledge is absurd, but the ideal of classic science rationality is necessary and valid, but insufficient to comprehend reality in current times. It is necessary a new paradigm of rationality which allows thinking the unit of fragmented knowledge in disciplines related to human species survival in this era which has become planetary. This reflection presents from Edgar Morin's (complex thought) and Basarab Nicolescu's (transdisciplinary knowledge) conceptual proposals, the epistemological, ontological and methodological dimension of the emergence of this new rationality.