Yes, I think that in the most general terms the uses of could / would / should / might can be classified as:
- past tense - I can go there today / When I lived in Brighton I could go to the beach every day
- subjunctive, i.e. tentative - Will you pass me the salt please? / Would you please pass the salt?
- and conditional - I will go to the shops / If I had my car I would go to the shops.
But as Cypherpunk says, so much idiom is attached to these words, and so much of that idiom attaches to one form and not to others, that it may not be particularly helpful for learners to analyse these words in this way.