According to Popper, scientific laws are hypothetical in character; they cannot be verified, but they can be falsified by testing. The key to the success of scientific method is that it can test generalizations of universal validity with the help of singular observations. One failed test is sufficient to falsify a theory but no amount of confirming instances is sufficient to verify. This is a brilliant solution to the otherwise intractable problem: how can science be both empirical and rational? According to Popper it is empirical because we test our theories by observing whether the predictions we derive from them are true, and it is rational because we use deductive logic in doing so. Popper dispenses with inductive logic and relies instead on testing. Generalizations that cannot be falsified, do not qualify as scientific. Popper emphasizes the central role that testing plays in scientific method and establishes a strong case for critical thinking by asserting that scientific laws are only provisionally valid and remain open to reexamination. Thus the three salient features of Popper’s scheme are the symmetry between prediction and explanation, the asymmetry between verification and falsification and the central role of testing. Testing allows science to grow, improve and innovate.