La psychologie est diverse, plurielle, les pratiques sont variées. Cela est dû, entre autres, à l’apparition récente de la discipline psychologie et de la profession de psychologue. Certes Lagache a postulé « l’unité » de la psychologie, mais au prix de distorsions conceptuelles qui échouent à réduire sa diversité. Et la référence à la « science » ne fait pas tenir ensemble les discours disparates. Les invariants de la psychologie sont notamment son appartenance aux sciences humaines, ainsi que le titre de psychologue (qui est une protection mais aussi une complication). On peut circonscrire un invariant en considérant une « position psychologique » comme « position transdisciplinaire ». La transdisciplinarité concerne ce qui est essentiel et qui dépasse la spécificité de chaque discipline. Elle s’oppose à la pluridisciplinarité, ainsi qu’au complémentarisme ou à l’approche intégrative. Elle suppose humilité et humanisme. La transdisciplinarité concerne l’invariant dans toutes les variations. Un autre invariant est la fonction sociale et politique de la psychologie. La psychologie attire un nombre considérable d’étudiants car elle a une fonction sociale. Tout le monde a besoin de la psychologie, et il faudrait distinguer la formation à la psychologie, pour tous, à un niveau Master, et la formation des psychologues qui devrait être portée à un niveau Doctorat. La psychologie a aussi une fonction politique. En tant que science humaine, elle est garante de l’humanité et de la subjectivité dans la cité. Elle doit s’opposer à la violence actuelle de la désubjectivation. Et les universités comme les écoles de psychologues doivent veiller à maintenir et à garantir non seulement la pluralité des approches, mais l’humanité de la psychologie.

Psychology is diverse and multifaceted, and its practices are varied. This is due, among other things, to the recent emergence of psychology as a discipline and of the profession of psychologist. While it is true that Lagache advanced the concept of the “unity” of psychology, it came at the cost of conceptual distortions that fail to minimize its diversity. And the reference to psychology as a “science” does not serve as a unifying element of the disparate discourses. Other attempts to unify psychology have emerged, such as the establishment of the “code of deontology”. But the latter must inevitably consider divergent conceptions, if only with regard, for example, to respect for the “psychic dimension” that it postulates in its preamble: not all psychologists have the same representation of the “psychic dimension”. References and practices are extremely varied, even within each sub-discipline or “specialty” within psychology. As a result, psychology is in an uncomfortable position, always fragile, and always threatened by every attempt to assert control over the profession and to adapt authoritarian domination by public authorities, such as those we are currently witnessing. The invariants of psychology have to be defined or constructed. The first is its rightful place in the humanities. It is transversal and fundamental. Psychology has always resisted attempts at annexation by medicine, for example, and must continue to do so. Another invariant is the legally protected title of psychologist. This is both a protection and a complication. If a qualifier is not added to the noun “psychologist”, there is a great risk that cases of imposture will develop, such as the idea that any psychologist could be therapeutic as long as he or she is a psychologist. Another invariant can be circumscribed or constructed by considering a “psychological position”: an internal position that would cut across all psychology's specialties and sub-specialties. This position would be “transdisciplinary” within psychology. Transdisciplinarity concerns that which is essential and exceeds the specificity of each discipline. It is opposed to pluridisciplinarity, complementarism or integrative approaches. It does not simply juxtapose or even articulate disciplines but strives toward the essential that cuts across all disciplines. The “transdisciplinary position” is an internal position that in no way requires expertise in, or even knowledge of, all disciplines, for it is the opposite of an omnipotent, omniscient position. It requires humility and humanism. Transdisciplinarity concerns the invariant in all variations. The “psychological position” would be based on the essential, the very heart of psychology, the common denominator of psychologies. This kind of identification could also be made for each of psychology's sub-disciplines or specialties. Another constant is the social and political function of psychology. Psychology attracts a considerable number of students because it has a social function. Everyone needs psychology, and a distinction should be made between training in psychology for everyone, at the master's level, and training for psychologists, which should be raised to the doctoral level. Psychology also has a political function. As a human science, it is the guarantor of humanity and subjectivity in society. It must oppose the current violence of de-subjectification. And universities, and schools of psychology alike, must take care to maintain and guarantee not only the plurality of approaches, but also the humanity of psychology.