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Natural Philosophy is an Economic Policy Card in Civilization VI.
Strategy[]
Natural Philosophy is the first Economic Policy which boosts something other than 
Gold or 
Production. It is naturally more efficient the more Campuses you have, but it also becomes progressively more efficient the larger their adjacency bonuses are. For example, a Campus with a bonus of +1 will gain another +1 from this policy (for a total of +2), while a Campus with a +3 bonus will reach a total of +6. Since every single point of a yield type counts in Civilization VI, and most of the time the gain is absolute rather than proportionate, Natural Philosophy will only be worth it if you have more than one Campus and/or your Campuses have good adjacency bonuses - otherwise, it won't be worth it to spend an 
Economic slot just to gain a modest 1 or 2 
Science.
Of course, you will also have to take into consideration whether or not you really need the Science boost. If you are already managing a fast technical progress, then it will probably be more worthwhile to go with other Economic Policies. On the other hand, if you are playing as the Greeks with their civilization ability Plato's Republic (additional Wildcard Policy Card slot in any government), then this card is all but a default peacetime pick. This holds particularly true with Classical Republic or Merchant Republic as your government.
This policy is a must when playing as Korea, as their Seowon has a base adjacency of 4 Science. Since this policy doubles Campus adjacency bonuses, this gives Korea a huge boost in Science. This policy will also impact Arabia's Madrasa, boosting the amount of 
Faith depending on the adjacency bonus of the Campus it is in.
Natural Philosophy can impact Production if you have chosen the 
Golden Age Dedication Heartbeat of Steam, which gives a Production bonus equal to the Campus adjacency. A Campus surrounded by Mountains under this condition would generate +12 Science and Production.
Civilopedia entry[]
From the days of Aristotle, natural philosophy was the study of the physical world, the first systematic “science.” Every other science – biology, physics, chemistry, astronomy, mathematics, and all – has its roots in natural philosophy, and most of Aristotle’s predecessors such as Parmenides, Heraclitus, and Democritus centered their beliefs on the natural order. Aristotle’s conceptions of the laws that govern the real world, set down in the Corpus Aristotelicum (the bits that survived), prevailed into the Middle Ages. Although the empirical study and understanding of everything would separate into various scientific disciplines, it all began with natural philosophy. And now the boundaries between the disciplines are getting blurry again.
