magamo Wrote:First off, the three words 空く, 開く, and 明く are the same word. They're just written differently.

There are tons of meanings for the word "get" in English as in "I don't get it (get = understand)," "Where can I get it? (get = obtain)," "He got angry (get = become)," etc. They're all spelled the same in English. But in Japanese you may spell the same word differently by using appropriate kanji for the intended meanings. So 空く, 開く, and 明く are one word just like all the "get"s are one single English word. They're not homonyms or homophones. If you look in a J-J dictionary for native speakers, most likely they're packed in the same entry while other あくs such as 飽く are treated as different verbs.

開く tends to be used when you use あく with a nuance of "open" or "start." Like you said, when あく is used for a door, probably it's spelled as 開く. When a shop opens, it's 店が開く. This "open" is sort of "start" in the sense that it starts operating. So sometimes 開く can be translated as "start" in some situations.

The kanji 開 can also imply that a hole or space becomes existent so that something can be entered to the other side. But 空 can also have a quite similar nuance, and there is no clear-cut line between them.

空く tends to emphasize the sense of empty space. There are many possible meanings and translations for 空く, so if you want to learn it in detal, look in a decent dictionary.