People have presuppositions, and they will live more consistently on the basis of these presuppositions than even they themselves may realize. By presuppositions we mean the basic way an individual looks at life, his basic worldview, the grid through which he sees the world. Presuppositions rest upon that which a person considers to be the truth of what exists. People’s presuppositions lay a grid for all they bring forth into the external world. Their presuppositions also provide the basis for their values and therefore the basis for their decisions.
— Francis Schaeffer, from How Then Should We Live?