So,while Willoughby considered politics (and particularly the study of the subject) to also encompass the description of political institution, the oxford dictionary included the word 'Science' in its definition. However, just how scientific the study of politics is (it is often called political science) has been a matter of keen dispute. Generally, science implies that knowledge is gained on a systematic, to orderly basis, permitting predictable and reliable propositions to be formulated. This method is more fully developed in the physical sciences; whereas politics, as one of the social sciences, is concerned with human behaviour. The complexity of individual human beings, the impact of experiments, difficulties encountered in the measurement and tabulation of political action and ideas, together with the ability of humans to learn and change behaviour , are factors which make it difficult to reliably predict political behaviour.