'aver sceso le scale' versus 'essere sceso dalle scale'

Question

What's the difference between credo di aver sceso le scale and credo di essere sceso dalle scale?

Answer 1

''avere'' is used for transitive verbs (like ''avere mangiato''), while ''essere'' is used for intransitive ones (like ''sono ammalato''). ''Scendere'' has two meanings, in the first case it's transitive and ''scale'' is the object of the action, so you use ''avere'', in the second case is intransitive and requires ''essere''.

This is the usual rule, but there are some cases where the choice is not straightforward:

http://www.treccani.it/magazine/lingua_italiana/domande_e_risposte/grammatica/grammatica_084.html