As of today, a monopole has not been detected in experiment. Hence, a monopole
theory is based on theoretical assumptions. Consider the following assumptions:

Electromagnetic fields of a monopole are identical to electromagnetic
fields of a charge.

A charge-monopole theory should be derived from the variational principle
and the charge-monopole duality relationship.

It turns out that assumption A leads to theories that are plagued with
inconsistencies. By contrast, assumption B enables the construction
of a consistent promising theory. More details can be found below.

The issues discussed on this page are written for physicists. Other
readers may read the second item. The first item shows a review
article published in the literature. Beginners may skip it and study
the other items first.