Full Idea
Freedom as the definition of man does not depend on others, but as soon as there is involvement, I am obliged to want others to have freedom at the same time that I want my own freedom.
Gist of Idea
When my personal freedom becomes involved, I must want freedom for everyone else
Source
Jean-Paul Sartre (Existentialism and Humanism [1945], p.306), quoted by Kevin Aho - Existentialism: an introduction 7 'Anything'
Book Reference
Aho,Kevin: 'Existentialism: an introduction' [Polity 2014], p.108
A Reaction
Appears to be a highly Kantian sense of rational duty, and a rather odd constraint on someone whose only value is freedom. Sartre is aware that he needs an existential politics, but he's not there yet. 'Involvement' is an interesting addition to Kant.