Lesson 13 · Pronunciation 4

Notice 

Now we compare the words for fish and man both for the plural and the singular form. Listen to the pronunciation. The sound remains short. Notice also that the last letter of the singular form is doubled. This in fact is the reason that the short-a and short-i remains short.

Listen to maan → manen and man → mannen. In manen, the first syllable is open: ma-nen. The a keeps its long sound and is written once. In mannen, the doubled consonant closes the first syllable: man-nen. The a stays short. A single vowel before n is not automatically long: compare man.

The same spelling pattern appears in boot → boten and pot → potten.

As we said before, the same holds for the letter o. If we deal with a long-o like in the Dutch word "poot" (for example, the leg of a dog), the plural form becomes "poten" and we still hear a long-o, whereas with potten (2 t's) the sound  remains short.