In 1737 he published a special work to explain this conception: the Observations on the Continuous Progress of Universal Reason.
He recurs to the comparison of the life of collective humanity to that of an individual, and, like Fontenelle and Terrasson, accentuates the point where the analogy fails.

We may regard our race as composed of all the nations that have been and will be--and assign to it different ages.
For instance, when the race is ten thousand years old a century will be what a single year is in the life of a centenarian.

But there is this prodigious difference.

The mortal man grows old and loses his reason and happiness through the enfeeblement of his bodily machine; whereas the human race, by the perpetual and infinite succession of generations, will find itself at the end of ten thousand years more capable of growing in wisdom and happiness than it was at the end of four thousand.
At present the race is apparently not more than seven or eight thousand years old, and is only "in the infancy of human reason," compared with what it will be five or six thousand years hence.

And when that stage is reached, it will only have entered on what we may call its first youth, when we consider what it will be when it is a hundred thousand years older still, continually growing in reason and wisdom.
Here we have for the first time, expressed in definite terms, the vista of an immensely long progressive life in front of humanity.