English semantics

These word pairs have essentially the same meaning, but differ in semantics by a distinction that isn't made in certain other languages I know. This makes these distinctions lexical selection issues in machine translation.

say, tell

• "say" takes as a required complement the utterance/thing said; the person told is optional
• "tell" takes as a required complement the person told something; the utterance/thing said is optional

since, starting

• "since" means something is still ongoing
• "starting" doesn't mean it's still ongoing

watch, look at

• "watch" if something changes or has the potential to change
• "look at" if something is static

hurry up, be quick

• "hurry up" if activity has already started
• "be quick" if activity hasn't started yet

out, outside

• "out" = not at the house = somewhere else
• "outside" = not in the house = but often at the house (i.e., not out)

before, until

• "before" if event has a stage that can start or end preceding reference event
• "until" if event has stages or iterations that can continue preceding reference event and end upon reference event

Or maybe it's just about the presence ("before") or absence ("until") of a gap of time between the event and the reference event.

that's why, so

both explain that the thing before is a reason for the thing after, but they differ in their uses:

• "that's why" if you've already talked about the thing after it ("that's why I went shopping")
• "so" if you haven't already talked about the thing after it ("so I went shopping")

even though, even if

• "even though" makes the matrix phrase depend on something that actually happened/happens/will happen
• "even if" makes the matrix phrase depend on something that is only hypothetical