"Opticks" differs in many respects from the "Principia". It was first published in English rather than in the Latin used by European philosophers, contributing to the development of a vernacular science literature. The book is a model of popular science exposition: although Newton's English is somewhat dated—he shows a fondness for lengthy sentences with much embedded qualifications—the book can still be easily understood by a modern reader. In contrast, few readers of Newton's time found the "Principia" accessible or even comprehensible. His formal but flexible style shows colloquialisms and metaphorical word choice.