de quoi s'agit-il? What is the matter? Compare

the Latin rcs agiticr, in which the 'thing in question ' is the subject of the passive verb, whereas it is in French the indirect object of the impersonal retlexive verb ; and note that the use of the verb to be in the conjugation of ail French reflexive verbs is due to their assimilation with passive verbs already existing in Latin verbs and generalised wlien the French language (formed from the Latin) passed from a synthetic to its présent analytic state.