Edit: I’ve realized this definition was wrong and sleep-deprived and that the actual definition I use is: “This” refers to within this 7-day period of Su–Sa, “Last” refers to the last 7-day period, and “Next” refers to the next 7-day period. I was depriving myself of sleep to finish some work and came up with this. So “this” remains the same, but I just made up some definition of “next” that’s inconsistent with how I’d describe months in years. Hopefully the work is okay.

• “This Thursday” is for the Thursday contained within the Sunday–Saturday interval you’re currently in.
• “Next Thursday” means, starting from 00:00 on a given Thursday, the first Thursday you hit (not including the one you’re on if applicable) as you go forward in time from that point.
• They aren’t mutually exclusive.

Is this not universal? It seems so obvious.

• If it’s a Friday, “this Thursday” is the one from a day ago, and “next Thursday” is six days from now.
• If it’s a Tuesday, “this Thursday” and “next Thursday” are both two days from now.
• If it’s a Thursday, then “this Thursday” is today (albeit weird), and “next Thursday” is seven days from now.
• And “Thursday next week” if it’s Tuesday is the Thursday nine days from now