Principles and rules of classification are studied under 

Principles and rules of classification are studied under taxonomy.

Any new organism discovered is first identified and named basis the nomenclature and is classified depending upon its characteristics and nature. This is done by the rules followed in the taxonomy. Taxonomy is the study of the rules and processes for grouping all currently recognised species into categories based on similarities in their origins, behaviours, and physical characteristics. Its three main goals are identification, nomenclature, and categorization. Linnaeus is said to be the father of taxonomy system.