Natural science – a major branch of science that tries to explain, and predict, nature's phenomena based on empirical evidence. In natural science, hypotheses must be verified scientifically to be regarded as scientific theory. Validity, accuracy, and social mechanisms ensuring quality control, such as peer review and repeatability of findings, are amongst the criteria and methods used for this purpose. Natural science can be broken into 2 main branches: life science, and physical science. Each of these branches, and all of their sub-branches, are referred to as natural sciences.