As amazing as his science was, some of his assumptions about the natural world were deeply flawed. Newton was a frequent alchemist. One of his ultimate dreams was to finally figure out how to make gold. We know in the modern day that alchemy is essentially a made-up science (something not really known in the day), but despite his incredible contributions to mathematics and science (both 10s, in my book), I feel that I cannot rate him higher than a 6 or a 7 (I chose a 6) in philosophy because of this.
Sir Isaac Newton PRS MP (25 December 1643 – 20 March 1726/7) was an English physicist and mathematician (described in his own day as a "natural philosopher"). His book Philosophiæ Naturalis Principia Mathematica ("Mathematical Principles of Natural Philosophy"), first published in 1687, laid the foundations for classical mechanics. Newton made seminal contributions to optics, and he shares credit with Gottfried Leibniz for the development of calculus. More: en.wikipedia.org.