Might anyone know a rule to differentiate morphologically between verbs taking an infix (e.g. -ez- in "a lucra") and those that don't? I think in some cases the infix is what differentiates the verb from its substantive form, e.g. "a lucra" without infix would conjugate to "eu lucru," "a studia" would conjugate to "eu studii," but I am struggling to come up with a morphological rule. I know of several studies that may address this question but I haven't found them online.