WordNet sense 1 (the reasoning involved when you assume the conclusion is true and reason backward to the evidence):

reasoning backward

WordNet sense 2 (go back to a previous state):

return, revert, retrovert, turn back

WordNet sense 3 (get worse or fall back to a previous condition):

retrograde, retrogress

WordNet sense 4 (returning to a former state):

regression, retrogression, reversion, retroversion

WordNet sense 5 (go back to bad behavior):

lapse, relapse, recidivate, relapse, fall back