As people left the constraints of religious dogma, they began to question nature and to society and to look for for cause and effect relationships. This gave rise to a re-birth of logical inquiry, the scientific method, and a new view of the individual as a rational, thinking person.
Rationalism has its roots in the Greek philosophers such as Plato and Aristotle, but flowered during the Enlightenment. It is based upon the idea that knowledge can be developed through logic and experience and does not require "belief". During the Enlightenment, it was closely related to Empiricism and the two were considered virtually the same during the period and did not diverge philosophical paths until later. Generally, the British philosophers tended to be Empiricists and the continental philosophers tended to be Rationists during the 17th and early 18th centuries.
This essentially broke the paradigm that all knowledge flowed from a deity or some form of a holy book and established the paradigm that rational thought and there science could discern cause and effect relationships and build knowledge. This new paradigm gave birth to the scientific method as well as to a new view of society.
The rise of scientific inquiry gave rise to critical institutions such as The Royal Society, which fostered science and critical thinking. The Royal Society would have been unimaginable before the Enlightment. As late as the Elizabethan times, mathematics and science were often equated with "black magic".
With this new mode of inquiry, philosophers were now able to consider not only natural phenomenon such as Benjamin Franklin and electricity, but turn their thoughts to the organization of society. The philosophers shown in the figure above, on both the Empiricist and the Rationalist side all contributed to a new way of looking at the individual and society based on a rational or empirical view rather than a theological view. This analysis directly threatened monarchies and other forms of government that centered all power in a governing class that exerted this power, with little or no restaints over the people.
The divorce of rational thought from the constraints of religion, however, did not necessarily mean that Rationalists were atheists. Many remained profoundly spiritual, but their spiritual outlook was different than the mainstream religions. It tended to encompass either a Deity that was more accessible and rational than in many religions or more remote and uninvolved with the day-to-day workings of the Cosmos. The former often took the form of Pantheism while the latter took the form of Deism.
Pantheism is often confused with polytheism, but is distinctly different. The essence of Pantheism is that Deity is immanent and infused in everything. That does not mean there are many gods. It simplies the Divine is within all and accessible to all.
The popular image of Deism is of the clockmaker who builds a clock and then moves on to other projects and lets the clock run by itself. At the extreme, it can mean a Deity that is uninvolved with the Cosmos and is remote and potentially unaccessible. For other Deists, the Deity does not interfere with day-to-day activities, but is present, watching, and potentially accessible.
Several of the founders where Deists or possibly Panthiests. In the Declaration of Independence, Jefferson refers to "Nature's God". Jefferson clearly believed in the moral aspects of Jesus, but not what he considered, the "supernatual aspects". His Jefferson Bible essentially strips out these aspects and leaves a rational, moral Jesus. This concept is entirely in line with a Rationalist perspective. It does not however, mean that Jefferson or other Rationalists thought they had to enforce this perspective on everyone. Jefferson endeavored to be tolerant of all religions. In his Notes on the State of Virginia, he wrote:
The rights of conscience we never submitted, we could not submit. We are answerable for them to our God. The legitimate powers of government extend to such acts only as are injurious to others. But it does me no injury for my neighbour to say there are twenty gods, or no god. It neither picks my pocket nor breaks my leg.