Basarab Nicolescu, 2002:

"As the prefix trans indicates, transdisciplinarity concerns that which is at once between the disciplines, across the different disciplines, and beyond all discipline.  Its goal is the understanding of the present world, of which one of its imperatives is the unity of knowledge.  

Is there something between and across the disciplines and beyond all disciplines?  From the point of view of classical thought there is absolutely nothing.  The space in question is empty, completely void, like the vacuum of classical physics.  Even when the pyramidal vision of knowledge is renounced, classical thought considers each fragment of the pyramid that is generated by the disciplinary big bang as an entire pyramid; each discipline claims that it is sufficient unto itself.  From the point of view of classical thought, transdisciplinarity appears absurd because it has no object.  In contrast, within the framework of transdisciplinarity, classical thought does not appear absurd; it simply appears to have a restricted sphere of applicability."

-Basarab Nicolescu (2002:44), Manifesto of Transdisciplinarity. (Trans. Karen-Claire Voss) State University of New York Press, Albany 2002.