Past forms of modal verbs
Modal verbs do not have different forms, so there is no past form. This means that we have to use a different construction if we want to use a modal verb to talk about a past situation.
Use a different modal verb
With some modal verbs, we can use a different modal verb to show that we are talking about a past situation:
will -> would
They will usually ask for a deposit. – Zwykle proszą o zaliczkę.
I will go to Warsaw. – Pojadę do Warszawy.
They would usually ask for a deposit. – Zwykle prosili o zaliczkę.
I would go to Warsaw every day. – Codziennie jeździłem do Warszawy.
can -> could
We can only go out at weekends. – Możemy wychodzić tylko w weekendy.
I can go to the party. – Mogę iść na imprezę.
We could only go out at weekends – Mogliśmy wychodzić tylko w weekendy.
I could go to parties when I was a teenager. – Kiedy byłem nastolatkiem mogłem chodzić na imprezy.
You should remember that would and could are not the past forms of will and can. Using these modals to talk about the past is only one of the ways in which they are used and they have other uses e.g. would in unreal conditionals or could in polite requests.
It would be wonderful if they came. – Byłoby cudownie, gdyby przyszli.
Could she spend the night with you? – Czy ona może przenocować u ciebie?
The verbs have to and need to are exceptions. They are not true modal verbs and are called semi-modal verbs. Both verbs have the same meaning, but need to is a little more polite and is often used in a business environment between colleagues.
Because these verbs are not true modal verbs, they have a past form.
have to -> had to
Candidates have to be EU nationals. – kandydaci muszą być obywatelami kraju należącego do Unii Europejskiej.
Candidates had to be EU nationals. – kandydaci musieli być obywatelami kraju należącego do Unii Europejskiej.
need to -> needed to
Candidates need to be EU nationals. – Kandydaci muszą być obywatelami kraju należącego do Unii Europejskiej.
Candidates needed to be EU nationals. – Kandydaci musieli być obywatelami kraju należącego do Unii Europejskiej.
For other modal verbs we have to use a special construction.
modal verb + have + Past Participle (3rd form)
We should be there by six o’clock. – Powinniśmy tam być o szóstej.
We should have been there by six o’clock – Powinniśmy byli tam być o szóstej.
We can use would in unreal conditionals, and this means that we can use this past construction for modals to make a past conditional without having to add adverbs or time phrases, as you do in Polish.
It would be perfect if they came. – Byłoby idealnie, gdyby przyszli.
It would have been wonderful if they had come. – (Kiedyś, w przeszłości) byłoby idealnie, gdyby przyszli.
It would have been wonderful if they had come yesterday. – Byłoby wczoraj idealnie, gdyby przyszli.