off the top of my head
- spontaneousArising without external cause
- improvisePerform without preparation
- brainstormSpontaneous idea generation
- guessEstimate without certainty
- recallMemory retrieval act
memory · think · rambling · unprepared · spur of the moment · ad lib · wing it · offhand · rough estimate · stream of consciousness · blurt · instinct · gut feeling · unrehearsed · extemporaneous · snap judgment · hunch · spitball
certainty and verification
off the top of my headfor certain
Beyond all doubt
definitively · for a fact · precisely · with confidence · authoritatively