Confusion on imperative forms?

Question

I have heard of all of the following conjugations as being imperative forms in Japanese by various texts.

なさる　→　なさい

くださる　→　ください

いらっしゃる　→　いらっしゃいませ

Are these all part of the same category of imperative forms? If so, are these irregular conjugations and/or are they distinct from the 「止まれ」-style imperative?

Answer 1

They are irregular conjugations. Copying from Wikipedia:

ござる・為さる（なさる）・下さる（くださる）・いらっしゃる・おっしゃるの5語は助動詞「ます」に続く時の連用形が「〜い」となる点が通常の五段活用動詞と異なる。「ござる」以外は命令形も「〜い」となる。規則どおりの「ござります」「なさります」などは、古風な響きとなる。

There is a sound shift to using い for both the 連用形 (masu-form) as well for the imperative form. As Wikipedia mentions, using the "correct" form sounds very old fashioned.

Here's another question about this:

• Proper form of なさる - なさります or なさいます