tong-
“to think, to feel”think/feel
PIE root meaning to think or to feel. Source of English "think," "thank," and words for cognition and gratitude.
Discussion
*tong- is a Proto-Indo-European root meaning "to think" or "to feel," underlying a remarkable semantic cluster in English that connects cognition, emotion, and social obligation.
English "think" derives from Old English þencan, from Proto-Germanic *þankijaną, with Grimm's Law shifting *t > þ. The same root gives "thought" (Old English þōht) and, crucially, "thank" (Old English þancian)—revealing that gratitude was conceived as a form of thinking about what someone has done. German denken ("to think") and danken ("to thank") preserve this same pairing.
The connection between thinking and thanking is not accidental but reflects a PIE conceptual framework where mental activity encompassed both cognitive processing and emotional-social response. To think about a favor received is to feel grateful.
The root may also appear in "methinks" (Old English mē þyncþ, "it seems to me"), where thinking shades into perception and feeling. Latin tongēre ("to know") has been proposed as a cognate, though this derivation is debated.
This root provides an important window into PIE psychology, where thinking, feeling, and social reciprocity were not sharply distinguished categories but aspects of a unified mental life.
Notes
Source of Latin "tongēre" (to know), English "think" via Germanic *þankjan.
Related Roots
English Words from *tong-
These modern English words descend from this root. Each page traces the full journey from PIE to present-day English.