An indefinite pronoun is a pronoun that does not refer to a specific person or thing, but rather to something that is indeterminate or undefined.
German has many indefinite pronouns. The only way to learn these is to go over them and practise using them in conversations. We can’t make you practise, but we can give you the tools to practice with!
These words are used in everyday speech to refer to someone in general. They are pronouns for an indeterminate or unknown person.
We often use them when the person or thing is not particularly relevant in the context that we’re talking in.
Jemand hat mir erzählt, Avocados seien sehr gesund.
The thing you have to keep in mind is that they are used when what matters is the information being transmitted. Who said it is irrelevant.
Some of these pronouns can also be combined with irgend-. This makes the whole thing even more indeterminate.
Hat irgendeiner meine Schlüssel gesehen? (...ganz egal wer, aber ich brauche die Schlüssel.)
Has someone seen my keys? (...it doesn’t matter who, but I need my keys)
Hat irgendjemand eine Kopfschmerztablette dabei? (... unwichtig wer sie hat.)
Has anyone one got some painkillers?(...it doesn’t matter who)
Jemand and niemand are only used in the 3rd person singular.
Man is always used in the third person singular, and it never changes. It can also only be used as the subject in a sentence, so it is always in the nominative case. Man is used to talk about someone that is undefined in a way that is slightly abstract. It’s kind of like the English “one” as in “one does or does not do something”, only in German it is a normal and indeed often used form, not something reserved for some very specific sectors of society.
Man hat oft keine Lust, nach der Arbeit noch Sport zu machen. "One" often doesn't feel like doing sports after work.
Man kann aber nach der Arbeit ein bisschen Deutsch lernen! "One" can study a bit of German after work!
In the accusative and dative cases, we use ein- or kein-. To talk in the negative form, we can also use niemand or keiner.
With ein- and its negative kein- we must always watch out for the case (nominative, accusative…) and the gender. The plural of ein- is welch-.
man, einer, eine, eins (one)
keiner, keine, keins (none / no one)
(irgend-)welche (some / someone)
Accusative and dative are also quite easy:
(irgend-)einen, eine, eins
keinen, keine, keins
(irgend-)einem, einer, einem
keinem, keiner, keinem
→ etwas/irgendetwas, nichts
Ich habe drei schwere Koffer dabei. Können mir (irgend-)welche helfen, sie zu tragen? I have three heavy suitcases. Can someone help me carry them?
Es ist keiner mehr zuhause. (Irgend-)Einer muss dann zwei Koffer tragen... und mein Rücken tut sehr weh...No one is at home. Someone must carry two suitcases...and my back hurts a lot...
Ach, egal! Ich trage sie. Grr... Man muss immer alles alleine machen...Never mind! I'll carry them. Grr...One must always do everything...
If we want to talk about a thing that is in the singular, about something or nothing, we use etwas/irgendwas/irgendetwas and nichts. These are always in the singular and they are not declinated.
Ist hier noch etwas unklar? Willst du noch irgendetwas wissen? Is something still not clear? Do you want to know something else?
Nein, gar nichts. Es ist alles klar! No, nothing at all. It's all clear!