In the sentence "der hatte doch eine Brille", why do we use 'der' instead of 'er'?

Question

Sie: „Der Mann da, das ist doch Walter.“
Er: „Walter? Nee, der hatte doch eine Brille.“
Sie: „Doch, das ist Walter.“

Can I say "er hatte doch eine Brille" instead of "der hatte doch eine Brille"? Why do we use der instead of er?

Answer 1

Sie: „Der Mann da, das ist doch Walter.“
Er: „Walter? Nee, der hatte doch eine Brille.“
Sie: „Doch, das ist Walter.“

Here, der is a demonstrative pronoun, which is used to shift the focus in a conversation to the male subject that was mentioned last.

Actually, the conversation is about two male subjects: a man not described further, and Walter. Using der, the speaker (er) emphasizes that he is now talking about Walter, and not about the other man anymore.

@Mark Lösche's view that using der was bad style, is wrong. I guess that he confuses the article der with the demonstrative pronoun der. In fact, the opposite is true: to not use the demonstrative pronoun der here would be considered bad style. If the speaker had used the pronoun er, then there would not have been an explicit shift of the focus, leaving room for ambiguity; the speaker could still have been talking about the other man.

Answer 2

In addition to Björn Friedrich's answer, which, at the time of writing, is the only one that explains a functional difference between the personal and the demonstrative pronoun, I would like to point out cases such as the following, where the demonstrative pronoun is preferred even in non-colloquial language.

Als ein Student Sokolow im März nach den Plagiatsvorwürfen fragte, ließ der ihn aus dem Hörsaal werfen und zusammenschlagen. (Badische Zeitung)

The demonstrative pronoun der is interpreted to refer back to the proximate antecedent, i.e. Sokolow (and not ein Student). If the sentence read ließ er ihn instead, the reader would at first glance assume that er referred back to the subject of the embedded clause, i.e. ein Student.

So er and der have overlapping, but distinct, uses.

Answer 3

In everyday German the personal pronouns er, sie (Sing. fem.), es, sie (Plur.) tend to be replaced by der, die, das, die. This applies also for accusative and dative forms:

Wo steckt eigentlich Peter? - Den hab ich vorhin im Garten gesehen.

Weiß Nicole, dass wir uns heute treffen? - Ja, der hab ich das gestern gesagt.

In German grammar these forms are called Demonstrativpronomen. Like personal pronous they are often anaphoric and refer to previously mentioned nouns.

Many people and many grammars say that demonstrative pronouns referring to persons are pejorative. Nevertheless in my region (Westdeutschland) it is absolutely normal to refer to previously named persons by those demonstratives, especially when they take position 1 in the sentence. It is colloquial, though, and spoken German. In position 3 you might use even in spoken German "normal" personal pronouns as well as demonstratives:

Ich hab ihn gestern angerufen und ihm Bescheid gesagt.

But if the person had been mentioned in the previous sentence, it would be more common for me to use a demontrative in position 1:

Weiß Peter Bescheid? - Ja, den hab ich gestern angerufen.

So, as an answer to the question, I would say that "er hatte doch eine Brille" is non-colloquial elevated style.

Answer 4

Using an article instead of a pronoun is very colloquial and even in spoken language it is often seen as bad style.

When someone in my family speaks of someone as der or die instead of using names or the proper pronouns, my parents promtply reply with

Der ist Wagenschmiere

or

Die ist Zwiebelmine

referring that it is bad style.

There is some kind of saxon proverb about it. I didn't find much about it except this as a part of Gotha dialect (in Thuringia). This marks the der as wordplay with Teer which means tar, as it sounds similar.

The point of this is to put more emphasis on the person in your sentence. So if you use the pronoun the emphasis is more on the object (Brille). An Alternative may be repeating his name to keep the emphasis on Walter as person:

A: Der Mann da, das ist doch Walter.
B: Walter? Nee, Walter hatte doch eine Brille!