Making a sentence that ends in なかった polite

Question

What are the different ways to make a sentence that ends in なかった polite?

Answer 1

Let's consider it in cases:

• If the 〜なかった is attached to a verb, then the correct polite form is 〜ませんでした (with the appropriate stem, of course).

• If the 〜なかった is attached to a noun or an adjective (both types), then the orthodox polite form is 〜ありませんでした. However, it is also common to see 〜なかったです for this.

• If なかった is being used as the main predicate, the polite form is ありませんでした. As above, 〜なかったです is also common.

For extra politeness, 〜でございます forms are used: e.g. 〜ございませんでした instead of 〜ありませんでした. Unlike 〜ありませんでした, it is possible to use 〜ございませんでした with i-adjectives, though the u-stem must be used, e.g. おはようございます, not **おはやくございます.

In the colloquial language, 〜んです is sometimes attached to plain forms to make them polite without necessarily having the usual explanatory connotations. This is regarded as incorrect in formal contexts.

Finally, I'll just note that 〜ないでした is universally regarded as wrong.