The association of the Past Tense with adverbials that tell us when something happened is very important. Adverbials used with the past tense must refer to past (not present) time. This means that adverbials which link the present (before now, so far, till now, yet) are not used with past tenses.

Some adverbials like yesterday, last summer and combinations with ago are used only with past tenses:

I saw Jane yesterday/last summer.

Ago, meaning 'back from now', can combine with a variety of expressions to refer to the past: e.g. two years ago; six months ago; ten minutes ago; a long time ago:

I met Robert Parr many years ago in Czechoslovakia.

The Simple Past is often used with when to ask and answer questions:

When did you learn about it? - When I saw it in the papers.

When often points to a definite contrast with the present:

I played football every day when I was a boy.

Other adverbials can be used with past tenses when they refer to past time, but can be used with other tenses as well:

adverbs: I always liked Gloria

I often saw her in Rome.

Did you ever meet Sonia?

I never met Sonia.

adverbial/prepositional phrases: We left at 4 o'clock/on Tuesday.

We had our holiday in July.

adverbial clauses: I waited till he arrived.

I met him when I was at college.

as + adverb + as: I saw him as recently as last week.