There are deviant cases, however, the most notable ones being found in the Slavic languages, where PFV:IPFV and PAST operate wholly independently of each other.

PAST takes us to the categories traditionally regarded as tenses. Among those, one category that comes close to being universally represented is FUTURE, which, however, scores lower on some other parameters of centrality, in being more often expressed periphrastically than e.g. PAST and being less often obligatory.