Reflective Pondering
Reflective pondering is the thinking half of rumination: deliberately turning inward to work out what actually happened and what you would do differently. Its twin, brooding, asks a question that cannot be answered. Both came out of a 2003 analysis by Wendy Treynor, with Richard Gonzalez and Susan Nolen-Hoeksema. Reflection is the half that did not predict worse depression in that paper, and it is also the half that has held up least well since.
What it is
At three in the morning the two halves feel identical. The difference is the shape of the question. "What did I actually say, and what would I say next time" is reflective. "Why am I like this" is brooding. Only the second of those reliably predicts getting worse.
The split came out of a psychometric analysis, which means the researchers took an existing questionnaire about how people respond to low mood and asked statistically whether all its items were measuring one thing. They were not. The items separated into two groups, and the two groups behaved differently. Credit belongs to Wendy Treynor as first author, not to the better known third name on the paper, and this site names her first every time.
This page is kept separate from the brooding page deliberately, because the evidence for the two halves is not equally strong and merging them would hide that. The popular version, good rumination against bad rumination, is a much tidier story than the data tell.