Verb imperative forms in German
Reading the descripsion of the Imperative skill, I want to ask for one clarification. It says there are three forms of imperative, these are 2nd person singular, 2nd person plural and formal. However, as I have learned, there should be one more form - 1st person plural, which is simply formed by switching the verb and the personal pronoun - so 'wir gehen' becomes 'gehen wir', which could be loosely tranlated into 'let's go!' (A similar expression is 'Lass uns gehen') So I want to ask is this a mistake of Duolingo or is it not used anymore?
Also, the descripsion of forming the 2nd person singluar imperative could be confusing, as it says:
'The first one is used to address one person informally. It is formed by dropping the infinitive ending -en and adding -e. More often than not, this -e ending is dropped, especially in spoken German. This form of the imperative does not include a personal pronoun.'
However, this would not work for strong verbs, so a better explanation would be that you form the declarative sentence and then drop the -st ending and pronoun. So nehmen - du nimmst - nimm.
I only wanted to point out some things that seemed iffy to me, feel free to correct me.
If the strong verb only takes an umlaut in singular/3, tha imperative does not take the umlaut. (like your example fahren fährt fahr)
For other strong verbs, it is better to start from the singular/3 (or singular/2) from (like nehmen, nimmt, nimm)
The 1st person plural, 3rd person plural, and 3rd person singular imperatives are formally a subjunctive.
Hence why we say Seien Sie! and not *Sind Sie!.
3rd person singular example: Lang lebe der König!
3rd person plural example: Seien x und y die Länge und Breite....
Sorry, I'm a little confused. Isn't "Seien Sie" 2nd person (formal, singular or plural)?
I'm not too familiar with grammatical words, but I just looked up "subjunctive", and one definition is: "relating to or denoting a mood of verbs expressing what is imagined or wished or possible." Is an imperative not always sort of a "wish"?
In English "Subjunctive I" refers to "Konjunktiv I", which is a verb form, not a "mood". When you say "a subjunctive" do you mean Konjunktiv I or do you mean the mood?
Seien Sie is a third person plural from a grammar point of view (using the same verb form and pronoun as "they" -- you can't hear the capitalisation).
The meaning is "you" (formal, singular, or plural), of course.
In relation to German, I've always considered the imperative (for commands) and the subjunctive (for reported speech etc.) separate moods.
Konjunktiv I is what might be called "present subjunctive" in other languages, i.e. present tense, subjunctive mood.
ich bin would be present indicative (i.e. present tense, indicative mood); ich sei is present subjunctive (i.e. present tense, subjunctive mood).
And then ich war is past indicative, ich wäre past subjunctive, aka Konjunktiv II.
All of those are "verb forms" (which I don't think has a formal definition), but two of them are in the indicative mood (bin, war) and two in the subjunctive mood (sei, wäre).
So with "subjunctive", I mean the mood "Konjunktiv", though commands such as sei Epsilon größer 0 or lesen Sie bitte das Buch are specifically in "Konjunktiv I" which is the present subjunctive, one tense of the subjunctive mood.
So "officially" there are only two imperatives, for du and ihr. I don't really sense a difference in "mood" between du/ihr and Sie. If you are giving directions to a friend you would use du, and if you were giving directions to a stranger you would use Sie. But the directions wouldn't be "commands" when you talk to your friend and a "wishes" when you talk to a stranger, would they?
No, there is no difference in "feeling", only a difference in how the commands are constructed grammatically. It does explain why you have to include the Sie in commands addressed to them but you do not include du or ihr in commands addressed to those.
Calling Konjunktiv II "past subjunctive" is kind of confusing. It's not usually used to talk about something that would have happened in the past. For example, "hätte ich genug Geld, flöge ich nach Deutschland" does not mean, "If I had had enough money, I would have flown to Germany". (or can it? I just read that Konjunktiv I and II can both be used for past and present)
In English you would say "let epsilon be greater than 0" or "suppose/assume epsilon is greater than 0". Since these are imperatives, I guess you could call them commands. But "sei Epsilon größer 0" is Konjunktiv I, so is it not like saying "I wish epsilon were greater than 0"? Really, you are just making a premise. The simplest way to say it would be "If epsilon is greater than 0" which isn't a wish or a command.