[mseebach]

Both the words "today" and "tomorrow" ("morrow" being related to the word "morning") are defined in terms of the day, not whether it's before or after midnight. "Noon tomorrow" spoken at 23:55 or 0:05 refers to the same point in time (~12 hours later) in human language. I would argue that "today" is basically unassigned at night - there is no current day in scope.

Sometimes we need to use non-human language to communicate intent correctly to a computer, but we shouldn't let that redefine perfectly good and well established human language.

[daveFNbuck]

This is how you use today and tomorrow. It's not universal to all human language or even to English speakers. Words have different meanings depending on lots of factors including context and region.

Your definition has the same issue that mine does, just with sunrise being the time around which the meaning of tomorrow is unclear. How high does the sun have to be before "today" becomes defined and the meaning of "noon tomorrow" shifts by 24 hours? If I wake up before sunrise, does tonight refer to now or to after the next sunset?

There's a certain amount of ambiguity inherent to the English language.

[mseebach]

Yes, there's ambiguity, but there's no reason to introduce new ambiguity where none existed before by trying to reason about these words in terms of midnight (possibly for the benefit of computers), when that was never where these words were anchored. That was the point I was trying to make.

[daveFNbuck]

I've always reasoned in terms of midnight because that's when the date changes. I use tomorrow to mean the next date and today to mean the current date. I'm not doing it for the sake of computers, that's just what I've always understood these words to mean.

I think using midnight as the anchor for the today/tomorrow distinction is a lot less confusing and ambiguous than having today/tomorrow not tied to the current date.