Leon Battista Alberti wrote 'Della Pittura' ('On Painting') in 1435.
He thought that art is the perfect combination of three things;
The humanistic-based means and aims - istoria,
the sensory detection of the play of light on a surface ie, the visible reality - la piu grassa Minerva,
with mathematics - la mathematica - as the means of controlling this visible reality.
Alberti does not present the painter with a rigid set of formulae, but puts the final outcome of the work of art in the hands of the artist. He would say that the end result of the exhaustive decisions that strive to achieve the elusive mean, is well worth the pains.
Addressing the patron/purchaser as well as the painter, he says:
'The istoria which merits both praise and admiration will be so agreeably and pleasantly attractive that it will capture the eye of whatever learned or unlearned person is looking at it and it will move his soul'.
Thus, the art will not only please the beholder but also touch him or her. It is to be effective, making a direct link between itself and the beholder. It is to affect both the art-educated and the uneducated. Alberti believed art is addressed not just to an elite; it is to reach everyone by the universality of its appeal. And should not be 'reserved for the bedroom of a merchant prince or petty tyrant' but is to be made public where all can see it.
It will make the painter's contemporaries 'judge him another god and will give him perpetual fame'; it will give the dead life, aid religion, and by its example raise the humane level of all men.
At the same time it is a profoundly humanist art, capable of expressing and satisfying the intellectual aims of both the princely patron and the artist.