No umlaut in some plural nouns

Question

Some masculine and neuter nouns don’t umlaut the last vowel in the stem of the word in the plural when it would be possible. What’s the historical reason for this?

Answer 1

In present-day German, masculine nouns with the plural suffix ‑e fall into two different declension classes, depending on whether they have umlaut or not. That is, for these nouns, umlaut is not predictable and must be learned.

suffix ‑e and umlaut: Baum – Bäume, Fuß – Füße, Gast – Gäste, Stock – Stöcke, …

suffix ‑e and no umlaut: Arm – Arme, Laut – Laute, Mord – Morde, Schuh – Schuhe, …

There is no single historical reason for nouns belonging to either class. For instance, although the umlaut of Gäste can be traced back to Old High German pairs such as gast – gesti (with umlaut triggered by the suffix ‑i), the same cannot be said for Bäume (OHG boum – bouma).

In the course of history, there has been a lot of variation with regard to how a given noun forms its plural. Remainders of these processes are still visible in words that have multiple ways to form the plural. For instance, both die Wagen and die Wägen is accepted.

Masculine nouns with no suffix in the plural behave similarly to those with ‑e treated above: umlaut is not predictable.

no suffix and umlaut: Graben – Gräben, Mangel – Mängel, Vater – Väter, …

no suffix and no umlaut (sg. = pl.): Kabel, Maler, Schatten, …

In all other instances, umlaut is predictable.

• Neuter nouns belonging to either of the two classes above (suffix ‑e in the plural or no suffix in the plural) do not have umlaut. There are a few famous counterexamples, but these are very much the exception that proves the rule.

• Feminine nouns belonging to either of the two classes above always have umlaut (where possible).

• For all other plural classes, umlaut is predictable: ‑er always has umlaut (where possible), ‑n and ‑s never have it.

Answer 2

There is no specific reason. Some people just preferred one of both versions and other people have copied them, and so one form became more frequently used and the other became extinct.

This happened to the majority of all nouns. But there are still some nouns that have two different plural forms, often with different meanings:

• der Mann
  • die Mannen; die Mann (alle Mann an Bord)
    (see also this question)
  • die Männer
• das Land
  • die Lande (durch die Lande ziehen)
  • die Länder
• das Wort
  • die Worte
  • die Wörter
• das Wasser
  • die Wasser (mit allen Wassern gewaschen)
  • die Wässer
• der Mund
  • die Munde (in aller Munde sein)
  • die Münder
• der General
  • die Generale
  • die Generäle (mainly in Austria)
• das Tuch
  • die Tuche (drapery, fabrics)
  • die Tücher (cloths, scarfs, ...)