English semantics

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