I wonder why they didn’t use “can” : “You can go and see them”
“You could go and see them” = It is possible, they are there, so they can be seen. The situation is possible.
“You can go and see them” = You are allowed to see them. Or, you have the ability to see them, you have eyes and are able to look at them.
Both meanings are quite similar, I think most native speakers could use both with the same meaning.
Thanks maths!!!
Yes, both have virtually the same meaning. Using “could” (as it’s conditional) makes it less severe / forcing / expectant and sounds a little more polite.
‘‘You can go and see them’’ is somewhat ambiguous. It can either involve an ability of the addressee (epistemic), as in reply to ‘‘I wish the paintings were exhibited at the local museum and not at the Alexey von Schlippe Gallery’’, or permission (deontic), as in reply to ‘‘Mum, can I go to the zoo and see the pandas?’’
Whereas ‘‘can’’ may function as a deontic and epistemic modal in both declarative and interrogative statemens, ‘‘could’’ may only have deontic meaning in interrogative statements when refering to the 1st and 3rd persons.
‘‘Could I speak to the manager?’’
Yes, you can.
(?)Yes, you could.
I don’t think it’s possible to interpret the sentence ‘‘Could you do me a favour?’’ as both deontic and epistemic.
I was thinking of the following situation:
A prisoner asks a guard ‘‘Could you give me some food?’’. I think it denotes willingness in that case, as in ‘‘Will you please give me some good?’’. Wouldn’t it be odd to interpret it as ‘‘Are you allowed to give me some food (by some higher authority)?’’?
What are your thoughts?
And talking about modals....
1)''Rapsyn may function as a link between the acetylcholine receptor and the agrin-binding dystrophin-associated glycoprotein complex.'' The writer thinks it's possible(epistemic). But years later, scientists may discover that Rapsyn never functions that way.
2)''The word ''can'' may be used in those cases''->Permission (deontic). It's allowed by (prescriptive) grammatical rules.
3)'' Whereas ''can'' may function as a deontic and epistemic modal...''-> Possibility (epistemic). It's one of its functions among many, but I'm not questioning the truth of these functions.
4)'' Whereas ''can'' can function as a deontic and epistemic modal...''-> Theoretical possibility(epistemic). I believe this is usually the case (and I like cacophony). ''Anybody can make mistakes'', ''It can be very cold in Stockholm''.
I think the meanings of the modals in 3 and 4 somehow overlap, but those in 1 and 4 don’t…So would you say there are 2 different epistemic uses of the modal ‘‘may’’?
Lawliete,
You know and understand more about English grammar and usage than 99.99% of native speakers.
Respect. 
Lawliete,
I haven’t a clue what you’re talking about, but it was nice to see a little bit of English subjunctive in your well-written post:
'I wish the paintings were exhibited at the local museum…"
@JayB: I still have a LOT to learn, and don’t be so harsh on native speakers of English. 
Thanks for the kind words, though!
@Jamie: Sorry, I didn’t mean to be obscure.
@ Both of you: By the way, I loved your posts in the thread on the subjunctive.
Respect.
PS: Jargon explained → ‘‘Epistemic’’ modality is basically related to matters of knowledge and truth value (how certain the speaker is of the truth of his/her statement). ‘‘Deontic’’ modality, on the other hand, has to do with norms/expectations/desires and how the world relates to them (v.g, if I think something ought to be different).
And I still don’t know whether there are two different epistemic uses of the modal ‘‘may’’ or not :S. According to the theory I’ve read there’s only one. However, if I understand the usage of the modals correctly, there may be two.