Most if not all the "Founding Fathers" were Freemasons. Freemasons would have been taught esoteric knowledge. In that knowledge they would have learned Hermetic Philosophy. In Hermetic Philosophy there are 7 "Truths". This is what the founding fathers were referring to when they mentioned "we hold these truths to be self-evident". Below is a listing of the 7 truths in Hermetic Philosophy.
1. The principle of Mentalism -The ALL is Mind, The Universe is mental.
2. The principle of correspondence - As above, so below:as below,so above
3. The principle of vibration - Nothing Rests;everything moves;everything vibrates.
4. The principle of polarity - Everything is dual,everything has its poles,everything has its pair of opposites,like and unlike are the same,opposites are identical in nature.
5. The principle of rhythm - Everything flows, out and in,everything has its tides,all things rise and fall,the pendulum-swing manifests in everything;the measure of the swing to the right is the measure of the swing to the left;rhythm compensates.
6. The principle of cause and effect - Every cause has its effect,every effect has its cause,everything happens according to Law;Chance is but a name for Law not recognized;there are many planes of causation,but nothing escapes the law.
7. The principle of Gender - Gender is in everything,everything has it's Masculine and Feminine principals. Gender manifests on all planes.
Genesis 1:27 So God created man(humans) in his own image, in the image of God he created him (humans), MALE and FEMALE he created them.
When one fully understands all these principles, then the truths become self evident. Also one will be able to read the Creation story in the Book of Genesis and see each one these principles as it pertains to the Days of creation including Adam and Eve.
The 7 truths can be found in a writing of the Kybalion. I provided a link to anyone that is interested in reading it.