Under the influence of my previous post, no doubt, I found myself wondering about ought and tense. Specifically, whether "I am obliged to A at t" (e.g., "I am obliged to teach at 9:30 am today") is a statement about two times—the present and t—or just a statement about t. On the one-time reading, "I am obliged to A at t" has the logical grammar of "At t, I will be obliged to A." On the two-time reading, the logical grammar is "Now, I am obliged to A at t.
The conclusion was that the two-time reading is correct. Here's an easy argument. The following is intelligible. You are not currently obliged to A tomorrow. But five minutes later you validly promise me to A tomorrow, and after you've made the promise, you are obliged to A tomorrow. Five minutes later, I release you from your promise. You are no longer obliged to A tomorrow. So you can change in respect of what you are obliged to do tomorrow. On the two-time reading, this makes perfect sense. At t0, it is not yet the case that you're obliged to A at t3; at t1 you are obliged to A at t3; then at t2 you cease to have this obligation to A at t3. But if the statement were solely about what happens at t3, then there could not be any change in respect of it, since what happens at t3 does not change in this back-and-forth way.[note 1] Moreover, that I am currently obliged to A tomorrow places constraints on what I may permissibly do today.