Avoir and etre

Question

I saw in the lesson that you say j ai Monte Les escaliers rather than je suis montes Les escaliers  why is this Paul

Accepted Answer

Hi Paul,
As explained in the following lesson -
https://french.kwiziq.com/revision/grammar/monter-can-be-used-with-avoir-or-etre-in-le-passe-compose-and-changes-meaning
it depends whether the verb 'monter' has an object (transitive) or not .
In this case it has - monter les escaliers - so it will take 'avoir' but if you said 
Je suis monté dans ma chambre = I went up to my bedroom 
it would be 'être' as it has not object (intransitive).
Hope this helps!