At the time, Franz Mesmer's theories on animal magnetism were popular on the upper circles of society. When confronted with the events described above, many scientists (including Rivail and some of his peers) pointed out that the animal magnetism could explain the physical effects observed. At first, Rivail thought that this was a good explanation for what he had heard. However, after seeing personally a demonstration, he quickly dismissed the animal magnetism thesis, as not to be sufficient to totally explain all the facts he observed. Rivail was determined to understand exactly what was the cause behind the physical effects popularly attributed to the spirits.

As an academic with a solid scientific background, Rivail decided to do his own research. Being not a medium, he compiled a list of questions, and started working together with fellow mediums and channelers to ask the spirits about them. Just as he did start to question the spirits, the quality of the communications improved dramatically. In 1857, Rivail (signing as Allan Kardec) published his first book on Spiritism, called The Spirit's Book . It comprised a series of 1018 questions, exploring issues related to the nature of spirits, the spiritual world, and the relationship between the spiritual world and the material world. It was followed by a series of books, the most important one being The Gospel According to Spiritism and by a periodic publication, the Revue Spirite, that Kardec published up to his death.

The name Allan Kardec appeared first when some of the spirits whom Rivail was communicating told him about a previus incarnation where he was a druid with that name. Rivail liked it, and decided upon using it, to keep his work as a spiritualist writer apart from his work as an academic.

Through his works, Kardec made clear that he was not proposing a new religion, but a new doctrine. The difference is clearly marked by the lack of formal structure or rites involving spiritist practice. In true Kardecist Spiritism, there are no rituals; a few practices are recommended, in generic terms, such as praying and doing charity work, but not specific gestures or words are ever cited. Most of the rituals that people observe today are derived either from later adaptations of the doctrine, or from mixups that resulted as people from different religious background started to accept and practice it.

Kardec defined spiritism as a practical science, hence the scientific aspect of the doctrine as defended by its followers. According to Kardec's own words, "spiritism is at the same time a observational science and a philosophical doctrine. As a science, it consists in the relationships that can be stablished with the spirits; as a philosophy, it comprehends all the moral consequences that can be caused by those relationships".

During the late 19th century, many well educated people from Europe and US embraced Kardecism as a logical explanation of themes related to the Christian Revelation. However, most of the initial enthusiasm receded. But in some places the work of a few dedicated preachers managed to achieve a solid foundation -- more notably, in Brazil, and to a certain extent in the Philippines. In Brazil, more than 2 million people declare themselves Kardecist spiritists, according to the last IBGE census data, which makes Brazil the largest Kardecist country in the world