A learning model is a description of the mental and physical mechanisms that are involved in the acquisition of new skills and knowledge and how to engage those those mechanisms to encourage and facilitate learning. Human beings have many different learning styles and most people can shift their styles in relation to the subject being studied but most also have a preferred style that works best in conjunction with their own talents, aptitudes and "mental wiring." The primary learning styles that exist are visual, auditory and kinesthetic (physical) learning. In recent decades many theories have been put forth due to the multiple methods available and the multiple learning styles that humans possess. This plethora of methods is subdivided into categories; behaviorism, cognitivism, constructivism, design-based, humanism and 21st century skills. Under each of these categories are numerous sub-categories to suit virtually any learning style.