All those who face this task agree on one point: it is not an easy thing! Why? To answer this question let us start with the very first words of a quote of Assagioli himself who stated: “We can first indicate (and not “define” because all definitions are limited and limiting), Psychosynthesis as …”  I would like to dwell for a moment on that distinction between “define” and “indicate” because it allows us to understand some fundamental aspects of the psychosynthetic approach.
“Indicate” vs. “define”: universality of language and primacy of existential experience.
The first point is the great care that Assagioli has always put in the choice of words. He was passionate about etymology, semantics and had fully grasped the symbolic value of language, therefore the importance of distinguishing the maps, the menu (namely the words), from the territory, from the dishes we are served, (namely the reality of experience that words want to represent), especially when it comes to an elusive reality like that of the human psyche. Words, as symbols, therefore, have the power to veil, and hide reality or reveal it. For Assagioli, the words capable of revealing reality are those that respect the fundamental criterion of universality: those that can reach as many individuals as possible, regardless of their cultural, ethnic, creed differences. Let’s proceed then in a psychosynthetic way: what is the difference in meaning between “define” and “indicate”?
To define (from the Latin “finis, -is”: border, delimitation of a field, and also end, death) means limiting, circumscribing, leading to end, solving, dissolving doubts: “It’s like that, period”.
To indicate (from the Latin “index, -icis”: he who indicates, who reveals) means instead to hint, show.We can define objects (which are inert, or “dead”), subjects instead (which are alive) can only be indicated, never fully grasped once and for all! In fact, we must consider Psychosynthesis as a subject in progress, an open, living and vital system, which develops by constantly interacting with the environment that surrounds it.
Reconstructing the etymological meaning of these two terms finally allows us to focus on one last point: the importance of existential experience as opposed to pure intellectual knowledge, certainly very useful but not sufficient. This is important: in Psychosynthesis, ideas and words should not stray too far from facts and actions. Knowledge that does not find direct application in daily life is sterile; the theory that does not alleviate the suffering is a dead letter. Assagioli has always given great importance to experience to the point of defining Psychosynthesis as “a life practice”. He said about his way of working: “I tried to be intelligent without being intellectual”. 
Fundamental aspects of the psychosynthetic approach: interdisciplinarity, interculturality and internationality
Starting from 1927, Assagioli then “indicated” Psychosynthesis in various more or less broad ways that I have organized starting from the more general and inclusive ones to conclude with the more specific and technical ones. He said: “We can first indicate Psychosynthesis above all as a movement, a tendency, a goal that translates into an attitude and a slow conquest towards (organization), integration and synthesis in every field: first of all, in the vast field of human knowledge to foster “the integration of psychology with other sciences, and with philosophy, religion and art.”
This is the first important characteristic that “indicates” Psychosynthesis: the interdisciplinarity, the constant dialogue between different points of view and of study that allows to overcome the fragmentation of knowledge and to have a more adequate overview of the complexity of reality.
The interdisciplinary approach is today more relevant than ever: the theory of complexity speaks of a new alliance between science and philosophy; quantum physics dialogues with the most ancient spiritual traditions; psychology with neuroscience, biology seems to demonstrate the presence of free will even in the invertebrates  etc.
But when Assagioli talks about integrating psychology with the other sciences, and with philosophy, spirituality and art what kind of psychology is he talking about? He speaks of a psychology which, in turn, is a “synthesis of all the positive, constructive elements existing in every school or psychological movement, with the aim of integrating American psychology (always looking for active and creative techniques and tools that are effective and efficient), with Europeanpsychology (so attentive to the investigation of the inner depths) and Easternpsychology (which, for thousands of years, has studied the transpersonal dimension of the human being and the realization of his most authentic Self). ” Today we could update this indication by adding the knowledge that comes from the other two continents, the indigenous psychology, the different shamanic psychologies, the ethno-psychiatric approaches, that had not yet developed in Assagioli’s times. So, after interdisciplinarity, the second important characteristic that “indicates” Psychosynthesis is internationality, interculturality. Also, very topical one. Assagioli’s intention was probably to create a breathing planetary psychology.
 R. Assagioi, Lo “spirito” della Psicosintesi (The “spirit” of Psychosynthesis), instruction letter addressed to Foundations, Institutes, and Psychosynthesis Centres in Italy and around the world., 11 Nov. 1967
 G. Dattilo, P. Ferrucci, V. Reid Ferrucci (edited by), Roberto Assagioli in his own words, Recorded by E. Smith, Ed. Istituto di Psicosintesi, Florence, 2019
 P. Guggisberg Nocelli, Conosci, Possiedi, Trasforma te stesso (Know, Master, Transform yourself), Xenia, Pavia, 2016
 B. Brembs, Towards a scientific concept of free will as a biological trait: spontaneous actions and decision-making in invertebrates, in Proceedings of the Royal Society B (Biological Sciences), Vol. 278, Issue 1707, 2010