 Models are a type of representation that involve abstractions and idealizations (Cartwright 1999; Chakravartty 2001; Weisberg 2012). Abstraction in a representation involves not including all of the properties of the thing represented and idealization involves distorting those features that are represented. That is, models delete and distort. Another important feature of models is that they indirectly represent the world. According to many philosophers of science, models describe mathematical or abstract objects, and these objects are more or less similar to particular objects in the world (Weisberg (2012), but see Hughes (1997; Odenbaugh 2014)). Theories as sets of laws represent the world directly because their propositional content is about natural systems. There are a number of different types of models used which include physical, scale, computational, and mathematical models.