Oh, wow, I have come to accept that verbs in Greek are very dynamic, but I was not expecting such a big change (είδα, δες, etc. are not even remotely recognizable as coming from βλέπω in my opinion). I guess, it is similar to how in English present tense "go" changes to simple past "went." Anyway, τώρα καταλαβαίνω, ευχαριστώ πολύ! :)
Yes, I imagine the origin is similar: that you have suppletion in action here, i.e. the various forms of what are now considered one verb were in origin several different words with similar meanings, which would explain the radically different stems.
(In English, the present tense of the verb that gave us "went" is still sort of around as "wend", as in "wend one's way".)
In French, "to go" is based on at least three different verbs: Latin ire contributed forms such as the future j'irai, vadere gave us forms such as je vais, and andare and/or ambulare gave us aller, allons, allez etc.
In ancient Greek βλέπω means to look at or watch, and εἶδον was an aorist-tense-only verb meaning to see, while a third verb, ὁράω, had present forms and meant to see.
εἶδον originally, in prehistoric Greek, was spelled with a digamma, viz. Ϝεῖδον, and was pronounced "WAY-don". This was essentially the same word as the Latin word video (pronounced "wí-day-o"), which is where we get the English word "video".
I can't think of a case where they can be interchanged while keeping the same meaning.
να can be used without a preceding verb but then it's more like "let's ...!" or "shall I ...?". For example:
- θα δούμε! - We will see!
- να δούμε! - Let's see!
- θα σου πω την αλήθεια. - I will tell you the truth.
- να σου πω την αλλήθεια. - Let me tell you the truth.
- θα ανοίξω το παράθυρο; - Will I open the window?
- να ανοίξω το παράθυρο; - Shall I open the window?
The former is second person singular and the latter is second person plural. Other than that, κοιτάζω is closer to look/watch and βλέπω = see, so I'd use κοίτα με for watch/observe, because it sounds to me like it matches the duration of the activity better than δες/δείτε. Δες/δείτε is good enough for just a glance, κοίτα/κοιτάξτε is not.
Most of the wonderful discussion here points out that Δείτε με! = see me or look at me, which implies, in English, short duration; longer than a glance to be sure, but still short. However, the translation above clearly states: ”Watch me!”, which in English implies longer duration. I can tell my child: “Look at me!” when I wish to have a serious conversation. On the other hand, I can say: “Watch me!” as I show him how to do something. Is the translation here correct?
I was red-carded just now when I translated this as 'Look at me.' ("Write this in English")(https://www.duolingo.com/skill/el/Verbs%3A-Imperative/practice)
I think I've lost something too. I don't remember seeing this verb before. Well, together with adverbs it opened the past, infinitive and imperative. I've chosen to start with the imperative. Should I have done the other way round? Where are the grammar explanations? They just opened in the first few lessons.