Model

A model is an informative representation of an object, person, or system. The term originally meant the plans for a building in late 16th-century English. It evolved through French and Italian before coming from the Latin word *modulus*. Models serve as tools to help us understand or predict the world. However, a model is not the same as a theory. While a model seeks to represent reality, a theory is more ambitious. A theory claims to provide an actual explanation of reality itself.

Physical models are tangible representations that differ in size from the original. These are often created through rescaling, meaning the geometry of the model matches the object. A model might be much smaller, such as an atom, or much larger, like the Solar System. Some models are even life-size, such as a fashion model displaying clothes. Sometimes, designers use systematic distortion in physical models. For example, they might use a larger scale for vertical height to better show mountains in topography.

Engineers use instrumented physical models to study fluid flows. They often use wind tunnels or water tunnels to test designs for vehicles or buildings. Some models are transparent to allow researchers to observe detailed flow phenomena. These models are scaled using specific principles like the Froude number or Reynolds number. In the pre-computer era, the UK economy was studied using a hydraulic model called MONIAC. This machine helped predict how changes, such as tax rises, might affect employment.

Conceptual models are theoretical representations of a system. They consist of concepts used to simulate a subject. For instance, weather models use differential equations to describe the atmosphere. These models are central to the philosophy of science. Most scientific theories effectively embed a conceptual model of the physical or human sphere. A physical model is often the reification of a conceptual model. This means the conceptual model acts as a blueprint before the physical one is built.

There are many specific types of models used in different fields. In logic, a model is a structure that satisfies a set of axioms, which are basic truisms. In computer science, a Large Language Model is an artificial neural network used for generative AI. Software uses the Model-View-Controller (MVC) design, where the model represents internal information. In biology, researchers use an organism as a model to study phenomena. For example, studying guinea pigs can help scientists understand scurvy without testing on humans.

According to Herbert Stachowiak, all models share three essential properties. The first is mapping, meaning the model represents an existing or imagined original. The second is reduction, where the model only includes attributes relevant to the user. A street map is a good example of reduction. It shows the course of streets but leaves out traffic signs to remain useful. The third property is pragmatism. This means the model is intended to work as a replacement for the original for specific subjects, times, or actions.

People utilize models for five general purposes according to Bruce Edmonds. One use is prediction, which involves anticipating unknown data through interpolation or extrapolation. Models also provide explanation by proposing mechanisms to explain patterns in data. They can be used for theoretical exposition to propose or refute new hypotheses. Models also serve for description by representing important aspects of a system. Finally, they are used for illustration to communicate complex ideas or explanations clearly.