Reflexive Verben. Example: ich streite **mich** mit dir?

Question

Consider the following example:

Er streitet sich schon seit Jahren mit seinem Nachbarn. (1.)

Here sich is singular. I would accept it (i.e. I would get the use of the reflexive form) if it were put in the following:

Er und sein Nachbar streiten sich seit Jahren. (2.)

Here sich is plural. What I do not get is the use of the reflexive form in singular when the reflexive action is clearly plural.

Another example:

Wo wollen wir uns treffen? (3.)

To me this is fine. I do not meet up with myself (unless we are in some philosophy books where the ego can be split in several parts, allowing for the possibility of meeting up with oneself). I am meeting with another person=> We are meeting EACHOTHER (≈uns).

Yet, there is also this usage of the reflexive form:

Er trifft sich mit seiner Freundin um fünf im Park. (4.)

sich here is clearly singular. Yet the reflexive character of the action is clearly plural. If one wanted to use the reflexive form, one would have to reconstruct the sentence making er and seine Freundin the new subjects:

Er und seine Freundin treffen sich um fünf im Park. (5.)

To reiterate: I get the usage of the reflexive form in plural (like in (2.), (3.) and (5.)). I think that's quite straightforward logic. What I do not get is sentences like (1.) and (4.). Are they two different forms to say the same exact thing, or is there a (subtle) difference in meaning?

P.S.: I am not talking about the reflexive verbs where the action is singular (e.g. Ich wasche mich). I am considering on those where grammatically the verb is singular, but the reflexive action includes several people.

Answer 1

Whether the verb and the reflexive pronoun is in singular or plural depends solely on the grammatical number of the subject. Or let me put it differently: The conjugation of the verb and reflexive pronoun always match.

Although in the following sentence there are two people involved, "er" is singular, thus the verb and the pronoun are singular:

Er streitet sich schon seit Jahren mit seinem Nachbarn.

On the other hand,

Er und sein Nachbar (plural) streiten sich seit Jahren. (2.)

And:

Wo wollen wir (plural) uns treffen?

The same applies to all your example sentences. But you ask:

Are the two different forms to say the same exact thing, or is there a (subtle) difference in meaning?

Yes, they mean basically the same. But that shouldn’t come as a surprise:

He argues (singular) with his neighbor.

He and his neighbor argue (plural).

Answer 2

Generally you just need to think of the reflexive 'form' of a verb as a separate verb entirely. 'Sich mit jdm verstehen' means 'to get on with sb', and is thus different from verstehen on its own which just means to understand.

Treffen on its own means to meet, but sich treffen more like to assemble or gather. Often making a verb reflexive changes the meaning in a way that is not initially obvious.

As for streiten vs sich streiten, to my knowledge there is no real difference in meaning, or at least certainly not in those contexts. Streiten can also mean to argue, but not with a named 'opponent', like to argue for something.

Griechische Journalisten streiten für ihr Recht auf Tarifverhandlungen

Greek journalists argue for collective bargaining rights.

Sich streiten can only really mean to argue specifically with somebody. But in your example they would have the same meaning.