  The occurrence of Simpson's paradox (SP) in $2\times 2$ contingency tables
has been well studied in the literature. The first contribution of the present
work is to comprehensively revisit this problem. We provide a threadbare
analysis of SP in $2\times 2$ contingency tables and present new results,
detailed proofs of previous results and a unifying view of the important
examples of SP that have been reported in the literature. The second
contribution of the paper suggests a new perspective on the surprise element of
SP, raises some critical questions for the causal analysis of SP and provides a
broad perspective on logic, probability and statistics with SP at its centre.
