“All for one, one for all—that is our motto, is it not?”
D’Artagnan turns the four companions’ alliance into a compact of mutual loyalty, making shared commitment more important than acting as isolated individuals.
Source details
The Three Musketeers, Chapter IX, “D’Artagnan Shows Himself,” Project Gutenberg #1257. D’Artagnan proposes “All for one, one for all” and Athos, Porthos and Aramis repeat the formula together immediately before Chapter X begins. The English wording is translated fictional dialogue and a solidarity motto within the novel, not Alexandre Dumas autobiography.