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Edward Hagen observes that critics of evolutionary psychology often argue that because a trait could have evolved as an adaptation or a by-product, it is impossible to determine which it is since it evolved in a past environment and thus evolutionary psychology hypotheses about a traits origin are untestable. According to Hagen, critics using this argument have a flawed understanding of science; Hagen argues that science is fundamentally an abductivist methodology e.g. inference to the best explanation. Hagen argues that hypotheses compete to provide the best explanation of a phenomenon, where "best" is measured via criteria like predicting new and surprising observations, parsimony, coherence and so on. Abduction does not require scientist to provide direct evidence for ever single prediction. Evolutionary psychology hypotheses make predictions and thus compete with other hypotheses to explain traits. Hagen further argues that while some critics conclude that evolutionary psychology explanations for mental traits cannot be true because they can't be tested for the above reasons, this is a false conclusion to draw; even if evolutionary psychology hypotheses could not be tested, this does not mean they are false, it just means the evidence for them could not be acquired, not that traits don't exist because of evolutionary reasons.