Question: What theory was put forth by the author of "Mathematical Principles of Natural Philosophy"?
Answer(s):
answer: Newton's law of universal gravitation

SPARQL query:
PREFIX ns: <http://rdf.freebase.com/ns/>
SELECT DISTINCT ?x
WHERE {
FILTER (?x != ?c)
FILTER (!isLiteral(?x) OR lang(?x) = '' OR langMatches(lang(?x), 'en'))
?c ns:book.author.book_editions_published ns:m.04v0x69 . 
?c ns:base.argumentmaps.innovator.original_ideas ?x .
}