Isaac Newton brought the Scientific Revolution to its completion.
He combined the empirical, inductive approach of Bacon with the
rational, deductive approach of Descartes; arguing that neither
experimentation without systematic interpretation nor deduction
without experimental evidence could lead to a reliable science.
This synthesis of the two approaches became the scientific approach
to knowledge that is still in use today. [For a description,
see the card on 'The Scientific Method', later in this history].
In addition, Newton invented 'differential calculus', which greatly
increased science's ability to use mathematics to model reality.
Einstein was to later call it the greatest advance in thinking
any individual has had the privilege to make.
The universe in Newton's model was very mechanical and deterministic. Given the present location, direction, and velocity of all matter in the Universe, Newton claimed that it would be possible to know exactly were every particle would be at any point in the future, and where it had been at any point in the past. His model was also very objective. The role of scientist as observer was assumed to have no effect on the operations of the observed, except for perhaps some minuscule gravitational effect that would be too small to measure.
By the end of the 19th Century, advances in measurement had taken physics into unexplored realms where Newton's mechanical, deterministic, and objective approach failed to explain the phenomena. Relativity and quantum theory took physics in an entirely new direction [described later in this history]. Psychology, however, has remained primarily Newtonian in its approach.