To my knowledge, German is the only language which capitalize the first letter of each of its nouns. Why is there such a rule?
Meines Wissens ist Deutsch die einzige Sprache, in der der erste Buchstabe eines Nomens groß geschrieben wird. Woher kommt diese Regel?
Capitalization of nouns was introduced in Late Middleages (14th century). The first letter(s) of single words (especially religious terms like "GOtt", but not just nouns) were set in majuscules in order to emphasize these words.
Today's capitalization of all nouns was officially introduced in 17th century German. The literary critic und translator Walter Benjamin:
“Das Barock hat in die deutsche Rechtschreibung die Majuskel eingebürgert.”
Though even centuries later capitalization has not been endorsed by everybody. Jacob Grimm commented in 1854:
“den gleichverwerflichen misbrauch groszer buchstaben für das substantivum, der unserer pedantischen unart gipfel heißsen kann, habe ich […] abgeschüttelt.”
See also:
You are correct in observing that German is probably the only language to still capitalise common nouns. (Note the emphasis)
First of all, this is because capitalisation can only happen in scripts such as Cyrillic, Greek or Latin which distinguish between capital and lower-case letters. Why they do that can probably be traced back to Charlemagne who allegedly let lowercase letters be invented — but that’s a story on its own (and for a different Stack Exchange). Point being that the vast majority of languages out there use an entirely different script and thus cannot capitalise anything.
Sometime during the Middle Ages to Renaissance, capitalisation of some nouns, later more, became popular across many European languages. At some point in time, most of them would capitalise at least some common nouns.
In the following centuries, it became fashionable to drop capitalisation again. I think Danish was the final language to drop common noun capitalisation in 1948.
But of course, the English capitalisation rules (English, Queen Elizabeth, Wednesday, cf French anglais, la reine Elizabeth, mercredi and German englisch, Königin Elisabeth, Mittwoch) also warrant discussion.
This rule helps to distinguish between sentences like this:
Er verweigerte Speise und Trank.
Er verweigerte Speise und trank.He refused food and drinks.
He refused food and drank.
Der Junge sieht dir ungeheuer ähnlich.
Der Junge sieht dir Ungeheuer ähnlich.The boy looks a lot like you.
The boy looks like you monster.
Wäre er doch nur Dichter.
Wäre er doch nur dichter.If only he were a poet.
If only it were more dense.
Vor dem Fenster sah sie den geliebten Rasen.
Vor dem Fenster sah sie den Geliebten rasen.In front of the window she saw the beloved lawn.
In front of the window she saw the lover raging.
Er hat in Berlin liebe Genossen.
Er hat in Berlin Liebe genossen.He has dear comrades in Berlin.
He enjoyed love in Berlin.
Not realy always complete sentence, but still good examples:
Warme Speisen im Keller
Warme speisen im Keller.Hot dishes in the cellar
Gays dine in the cellar.
Die Spinnen
Die spinnen.The spiders
They are crazy.
Beschädigte Liegen in meiner Filiale
Beschädigte liegen in meiner Filiale.Damaged beach chairs in my branch
The damaged lie in my branch.
Die nackte Sucht zu quälen
Die Nackte sucht zu quälen.The pure addiction to torment
The naked tries to torture.
Der Gefangene floh.
Der gefangene FlohThe prisoner fled.
The caught flea
Kürzlich habe ich auf Belles Lettres in einem Video-Tutorial* gehört, dass es damit zu tun hat, dass im Deutschen die Wortreihenfolge viel freier ist als in vielen anderen Sprachen. Dadurch hilft die Großschreibung von Substantiven der Orientierung beim Lesen.
Welches genau kann ich leider nicht sagen, sonst würde ich es verlinken.
Capitalisation of some (not all!) words makes sentences easier to read quickly, for much the same reason that ascenders (as e.g. in t, l, h, k) and descenders (as e.g. in g, p, q, y) do the same. Capitalising all nouns leads to a nice percentage of capitalised words and therefore aids reading.
I am not claiming that this is the reason we are doing this, but it's certainly a disincentive to changing it.
There was a time when capitalisation was pretty much random in most European languages. Then systematic rules developed out of the chaos. Capitalising all nouns would be more tricky or less consistent in English than it is in German, where adjectives or nouns preceding a noun are typically spelled together with the noun in a single word that can then be capitalised.
