When to use “depuis” and when to use “il y a” with time expressions

1.    Depuis I.        If you want to say you have done something since a certain point in time, you use depuis with the present tense. o  Je travaille comme professeur depuis 2017 >> I’ve worked as a teacher since 2017. II.        You can also use depuis to talk about a continuous action, which also translates to for: o  Je travaille depuis trois heures >> I’ve been working for three hours. o  Je travaillais depuis trois heures quand il est arrivé >> I had been working for three hours when he arrived. NB. There is no verbal construction in French to translate “have been/has been Ving”. Instead, we use the present tense in French. To translate “had been”, we use the imperfect. A period of time = for A precise point in time = since 2.    Il y a Whilst il y a can mean there is… …it can also be used to indicate something that happened in the past. o  J’ai fini mon travail il y a deux heures >> I finished my work two hours ago. o  Je suis allée à Lyon il y a deux ans >> I went to Lyon two years ago. NB. Il y a is used with the past simple, so is used to describe something that started and finished in the past.