Knowledge can be classified in different ways. Cross-classifications are possible. Below are given several criteria of classification that can be used. We can not say that one is better than the other. What matters is the purpose behind the classification.

ON THE BASIS OF THE METHOD OF ACQUISITION

INNATE AND ACQUIRED KNOWLEDGE: Innate knowledge is inborn. Acquired knowledge is acquired post-natally. Knowledge of good and bad is innate in humans however they can be confused. That is why acquired knowledge is needed to guide them in the gray areas. Acquired knowledge can be from revelation or from empirical observation. The two sources of acquired knowledge reinforce the innate knowledge as well as reinforce each other.

A PRIORI and A POSTERIORI KNOWLEDGE: A priori knowledge is knowledge not based on experience whereas a posteriori knowledge is based on experience. Innate knowledge is part of a priori knowledge.

ON THE BASIS OF SOURCE

RATIONAL and TRANSMITTED: Classically, knowledge was classified as transmitted knowledge which includes revelations and non-transmitted which includes empirical observation and rational reasoning

EMPIRICAL OBSERVATION: Knowledge can be classified as knowledge of the seen and knowledge of the unseen. Humans know only the seen. They do not know the unseen. The unseen can be absolute or relative. Humans cannot in any way know the absolute unseen except through revelation. The relative unseen is something that is knowable by humans by taking certain measures. For example the contents of a closed box are unknown by a human but when the box is opened, the contents can become known. It is however deceptive for a human to claim with certainty and affirmatively to know the contents of a closed box if he has no evidence through the senses.

ON THE BASIS OF LEARNING and USE

ON BASIS OF OBLIGATION: It is obligatory for women and men to get knowledge. This obligation differs for different types of knowledge. Some knowledge is considered a collective obligation. Other knowledge is considered individual obligation.

ON BASIS OF UTILITY: Knowledge can be useful. There is no concept of knowledge that is not useful but is harmless. Knowledge that has no immediate or foreseeable use is considered harmful. Sorcery is for example harmful knowledge. All correct knowledge is useful. However even useful knowledge can turn harmful is not used properly.

ON THE BASIS OF APPLICATION

Knowledge can be basic or applied. The distinction is sometimes more theoretical than real.

ON THE BASIS OF NATURE, CONTENT, and METHODOLOGY

ON BASIS OF LEGALITY: Most branches of knowledge are legal and are encouraged. For example study of medicine and science are legal pursuits. On the other hand study of sorcery is illegal because the knowledge is harmful. Between these two clear extremes are disciplines that are good or bad depending on how their knowledge is used. Study of the chemistry of ethanol is legal if it will be used for industrial purposes. It will rapidly become illegal if it will be used to make beer and other alcoholic drinks.