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Logic and math · experts disagree
The sorites paradox
Eubulides of Miletus, fourth century BC; the name is from the Greek for heap.
One grain of sand is not a heap. If you have some grains that are not a heap and you add one grain, you still do not have a heap: a single grain cannot be the difference between a heap and no heap. So two grains are not a heap, nor three, and by repeating the step a million grains are not a heap either. Yet a million grains of sand piled up is plainly a heap.
The argument runs the other way too: a million grains is a heap, taking one grain away leaves a heap, so one grain is a heap. Which part of the reasoning should you reject?