The belief in a God who created the universe and then abandoned it, assuming no control over life, exerting no influence on natural phenomena, and giving no supernatural revelation.
I would add that a deist would not believe in the incarnation of Jesus Christ. A deist would not believe that prayer is effectual. A deist would not believe that the books of the Bible were inspired by God. All these are instances of God entering into our physical universe and “influencing” it.
Therefore, if there is a public record showing a Founder offering up a prayer that God would intervene (i.e. in the American Revolution), this would be a proof that he is not a Deist.
Therefore, if it can be shown that any particular Founder took a public vow to a denomination that believed in the Incarnation, this is evidence he could not be a Deist.
Therefore, if there is a public record showing a Founder quoting Scripture, this would be evidence that he is not a Deist.
Founders denominations are researchable through their own autobiographical writings, the public record (i.e. the Congressional minutes), and their sworn public confessions of biblical faith before their church. Of this historical record, they are:
2 Dutch Reformed
2 Roman Catholics
3 deists: Williamson, Wilson and Franklin.
From the breakdown, we should be very impressed with similarity of the Founders’ beliefs. 49 were professed Protestants and 51 were professed Christians (93%). A 93% Christian population is not what anyone today would call a “diverse” crowd.
At this point something has to be said of the above evidences concerning this subject:
In a legal-historical context, the actual recorded words of any historical figure are the “best testimony we have” as to the veracity of the that figure’s heart. As in a court of law, a witness may testify under oath. The jury is constrained to believe that his words are true, unless there is other reasons to believe otherwise. As in my everyday conversations with people, their spoken or written words I will take as the affirmation of their beliefs, unless reasons to believe otherwise are introduced.
There are no reasons that I would take the Founders’ recorded words (or vows) any other way. For any objector to say of a historical figure “he really didn’t mean what he said”, and then not back it up with evidence, would be intellectually disingenuous.