Science has long been divided into two schools to describe its different functions -- descriptive and normative. In any scientific enquiry a scientist can be said to be taking a descriptive approach or a normative approach. There are fields of science that are either described as descriptive fields or normative fields. Generally speaking descriptive science takes an experimental and factual approach and seeks to establish clear and observable facts while normative science seeks to explain and improve on things. Fields such as physics or biology are classified as descriptive, while fields such as ethics are classified as normative although descriptive scientific method can be used in these areas as well.
Descriptive sciences aim to describe, measure understand and record the actual measurable realities around us. They are such sciences as have an experimental approach to their methodology such as chemistry or physics. They produce observable and unfaltering facts and measurements such as ‘water is made up of two parts hydrogen and one part oxygen.’ The purpose of descriptive science is to discover how the world, or how things really are, i.e. what do we really actually know through verifiable measurements.
Descriptive enquiry methodology uses experiments and measurements. Descriptive sciences seek to establish verifiable facts by demonstrating consistent results through repeated experiments. In the case of ethics or philosophy, it seeks to establish facts as to how people behave or think by measuring observable quantities, such as using statistics to know how many people suffer from a certain mental condition, or hold certain moral values.
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Normative sciences are evolving and seek to discover the way things should be. In areas such as ethics it will ask questions such as ‘is the death penalty right?’ whereas descriptive sciences will seek only to discover facts such as ‘what percentage of people believe the death penalty is right?’ Normative sciences seek to discover ‘good’ ways of doing things, or the ‘right’ way of thinking. The three recognized normative sciences are aesthetics, ethics and philosophy.
To make decisions or pronouncements on whether something is ‘good’ or ‘right’ normative sciences must operate within a set of norms or prevailing beliefs. They must know how people already think and behave, what their beliefs and thoughts are in order to establish the norms within which they can make what are essentially value judgements. Normative sciences find out how things are and then seek to improve on these things.