The following 12 basic principles of animation were developed by the 'old men' of Walt Disney Studios, amongst them Frank Thomas and Ollie Johnston, during the 1930s. Of course they weren't old men at the time, but young men who were at the forefront of exciting discoveries that were contributing to the development of a new art form. These principles came as a result of reflection about their practice and through Disney's desire to devise a way of animating that seemed more 'real' in terms of how things moved, and how that movement might be used to express character and personality. (http://minyos.its.rmit.edu.au/aim/a_notes/anim_principles.html)