He invented new forms of abstraction and standards of beauty to match them. (twocoatsofpaint.com)
In those days, the most known form of abstraction is what we would nowadays call «hard - edged» abstraction. (aaa.si.edu)
Over the course of his career, he evolved from creating abstract gestural works, in which he drew inspiration from the natural world, to a pure form of abstraction. (artzine.com)