Thinking, against going round again
Both feel like work. Only one of them arrives anywhere. Three ways to tell which one you are doing while you are doing it.
Thinking narrows. Rumination circles at the same width.
Both of them feel like work
You can spend forty minutes on a problem and come out of it tired, having been entirely occupied the whole time, with nothing you did not have at the start. That is rumination, and the reason it is hard to stop is that from the inside it is indistinguishable from effort. It has all the sensations of thinking: concentration, seriousness, fatigue.
The only thing it lacks is movement.
The first test: does it narrow?
Thinking narrows. You start with a problem the size of a room and after twenty minutes it is the size of a table, because the thinking has ruled things out. Even bad thinking narrows, just in the wrong direction.
Rumination circles at the same width. Twenty minutes in, the problem is exactly as large as it was, usually with the same three considerations cycling in the same order. If you cannot say what you have ruled out, you have not been thinking.
This is testable in the middle of doing it. Ask what is smaller than it was ten minutes ago. A blank is an answer.
The second test: is there a next move?
Thinking produces the next move, even when the next move is small or unwelcome. "I need to ask her directly." "This cannot be done by Friday and I have to say so." "I do not have enough information and the information is obtainable."
Rumination produces verdicts: that was stupid, they are difficult, this will not work. A verdict feels like a conclusion and cannot be acted on, which is precisely why it can be returned to indefinitely.
Any thought you can have again tomorrow without anything having changed is not a thought you finished.
The third test: is it about something that has happened?
Thinking is mostly about what to do. Rumination is mostly about what occurred. That asymmetry is the most reliable of the three tests, because the past is inexhaustible: you can always find another angle on a conversation from Tuesday, and none of them change Tuesday.
There is a real version of looking back, and it is short. What happened, what I would do differently, what that means for the next one. Three sentences. If it has taken longer than that, it has stopped being review.
What to do when you catch it
Not "stop", which does not work and adds a failure. Three things do work, roughly in order of how much they cost.
Write it down. Rumination depends on the thought staying slightly out of focus; on paper it is either a problem with a next step or it is visibly the same four sentences. Both outcomes end it.
Move. Not as a metaphor. A circling state is partly physical, and a walk interrupts it more reliably than a decision to think about something else.
Say it to somebody. Out loud and to a person, rumination collapses fast, because the social requirement to make a point forces the thing into a shape. Half the time you hear the answer while saying the question.
When circling is the right thing to do
One exception worth naming. Some problems are not ready, and the mind returning to them is not rumination, it is waiting with the file open. The distinguishing feature is that each return brings something slightly new.
The test is the same as the first one. Does it narrow? If each pass adds a detail, leave it alone. If each pass is the same pass, the file is not open. It is stuck.