"Have we shown you our garden?"
Translation:Pokazywaliśmy wam nasz ogród?
Perfective verbs accent that something was done. Imperfective verbs accent that something lasted - like here the action of showing lasted some time but it doesn't have to mean that the action hasn't been finished. This question is probably about whether they have seen our garden or not so such translation can be proper. Depending on context, both perfective and imperfective verbs can be translated into Present Perfect, but also into other English tenses. Simply, Polish tenses are different than English ones and put accent onto other aspects of time. There is no one-to-one correspondence.
"Have we shown" sounds more like imperfective aspect to me, such as "Have we ever shown you our garden? [when? which time]" This sounds general and unspecific.
On the other hand, "Did we show you our garden last time? [when? last time--specific]" This sounds like a perfective verb aspect.
I don't think it sounds correct to ask, "Have we shown you our garden last time?" The specificity of "last time" conflicts with the generality of "have shown." On the other hand, "did show last time" fits perfectly. Therefore "have shown" is present perfect tense, but the context of the sentence is an imperfective verb aspect.
"Have we shown" is the present perfect tense; "did we show" is the past tense. English doesn't have perfective and imperfective verbs. The verb aspect is determined by context. Polish on the other hand doesn't have past tense versus present perfect versus past perfect. It's all just past tense, but the verbs themselves have either perfective or imperfective verb aspects.
Well, as you note, we do have the present perfect "have you shown." We also have the past continuous "were you showing," which I think I would only ever translate as an imperfect. It is the English simple past "did you show" that tends to cause the problems. Here, though, I could picture translating "have you shown the garden" with either perfect or imperfect, depending on how I was thinking of the "showing."
Yes, exactly, it's open to interpretation in English, based on context, and past continuous does seem to have an imperfective aspect.
I was showing him our garden. Pokazywałem mu nasz ogród.
Present perfect usually leans on the imperfective side but can denote perfective in the context of the sentence.
I have shown him our garden. (In general, unspecific, BUT...) Pokazałem mu nasz ogród. (One time, at some point in time, OR...) Pokazywałem mu nasz ogród. (Numerous times in the past)
Simple past tense, though, in English could have either a perfective or imperfective aspect, based on context.
I showed him our garden yesterday [pokazałem]. I showed him our garden (unspecified) [pokazywałem].
In Polish you specifically use a perfective or imperfective verb to express the thought.
No, none of those. 'się' is a reflexive pronoun, so it doesn't make any sense here. 'cię' would be wrong case.
"pokazywać" takes Dative (you show sth TO WHOM?)
The Dative options for singular 'you' are either "ci" or "tobie". Actually, I'd use "ci" here, because I don't see any need to emphasize the pronoun. "tobie" is the emphatic version and it sounds kinda like "We showed him, we showed her... oh, and have we shown YOU our garden?"