In the philosophy of science, a theory is falsifiable if it is contradicted by "possible observations". These are any observations that can be described in the language of the theory, which must have a empirical interpretation. This latter condition says that the theory must be about concrete scientific evidence, while the former says that some (but not all) possible observations must be negating scientific evidence. For example, the statement "All swans are white" is falsifiable because "Here is a black swan" contradicts it.