Interdisciplinarity has its origin in sciences related to psychoanalysis and is based on the early works of Géza Róheim and Georges Devereux. It is supported on the need to cross the traditional boundaries between various disciplines, or between various schools of thought as a consequence of the emergence of new needs or the development of new theoretical or technical approaches.
However, transdisciplinarity crosses disciplinary boundaries in order to create a holistic approach. Recapping that holism is a methodological and epistemological concept whose postulate is to analyze systems and their properties as a single set and not only through the parts that make up this set. Therefore, transdisciplinary nature facilitates a systemic way of approaching a certain challenge. Contrary to interdisciplinarity, in transdisciplinarity, a deep knowledge of the disciplines involved and skills of moderation, mediation, association and knowledge transfer is needed for a transdisciplinary process to be successful. This means that transdisciplinarity focuses on problem solving by analyzing the problem as a single entity; like an everything.
Another way to look at the difference between these two concepts is to analyze the related concepts of transversal knowledge and longitudinal knowledge, or transversal knowledge discipline and longitudinal knowledge discipline. Cross-cutting knowledge areas are by definition interdisciplinary, and in merely theoretical or technical aspects they are supremely useful to methodologically approach a problem. But when this problem is related to human health, holistics forces us to take the longitudinal knowledge into account allowing us to carry out transdisciplinary processes. This is the reason why doctors have to study study medicine before underwent into a post-graduate formal education program. Medical Doctors may require about 600 academic credits to be sufficiently prepared in transversal and longitudinal areas of knowledge to carry out a transdisciplinary process.
In health, transdisciplinary process should be the rule, since it includes a patient holistic vision (the patient as a whole). Particularly when addressing systemic pathologies such as rheumatoid arthritis, diabetes, hypothyroidism, cancer, etc., the approach must be transdisciplinary. An orthopedist should not know how to perform an electromyography study, but should know how to understand the results and their interpretation. Therefore, medical knowledge must be transdisciplinary and in no way interdisciplinary.
