I have recently noticed something about a seeming shift in the way the adjectival suffix -alis was used over time. Earlier (that is, "Classical and earlier") formations such as aeternalis and nervalis displayed a dropping of the nominal/adjectival suffix, -us, from the stem (aetern- and nerv-, respectively) in suffixing with -alis. In later (Post-Classical) formations, however, such as Late Latin actualis and Medieval gradualis, there seems to have been an acceptance of reanalyzing the stem by considering the "u" of "-us" to be part of the stem (making the instant stems actu- and gradu-, yielding a somewhat different feel to the end products of the suffixation) in suffixing with -alis. Does anybody here know why this might have been...what the reason for such a change over time might be?