Piety
Faith is never identical with Piety
Faith is never identical with Piety
Introduction
Religions, especially organized religions, had a huge impact on civilizations and governments throughout our history. The Piety social policy branch, which could be adopted early in the Classical Era, describes various levels of influence and interaction between worldly and heavenly politics. By providing faith and culture benefits, Piety is a key branch for cultural victors.This branch cannot be active at the same time as Rationalism. Selecting Rationalism as the next policy of choice will result in one turn of Anarchy (production of almost all resources in the empire comes to a halt), and the effects of all social policies acquired in Piety will become inactive. Players are free to switch back and forth between Rationalism and Piety, but every switch will result in a new period of anarchy.
The Policies
General use
The Policies
Piety
Adopting Piety reduces the time to build Shrines and Temples by 50%. This branch cannot be active at the same time as Rationalism.Unlocking the Piety branch presents the player with doubled production when constructing faith buildings (Shrines and Temples). It could be quite helpful in early stages, where newly founded cities will mostly start building a Shrine, in order to get an early religion. However, Piety halves the time to build it, so it gets your cities a faster start. Similarly, fast Temples save mid-game production. Since Piety is available in Classical Era, adopting it earlier is essential, otherwise the production bonus gradually becomes less significant.
Note: this bonus is a production bonus, it's not making buildings cheaper. Every 10 hammers will be worth 20 hammers when building cultural buildings. It does not affect rush-buys with gold in any way.
Organized Religion
+1
Faith from Shrines and Temples.While the opener halves the time to build faith buildings, Organized Religion doubles the effect of Shrines and multiplies the effect of Temples by 1.5. With the opener and this policy, each new cities will get 2
per turn with 20 production cost. This bonus could be significant in early stages because it almost ensures that you could found a religion and enhance it quickly.
Mandate of Heaven
50% of excess
Happiness is added each turn to the amount of 
Culture that may be spent on Social Policies.This social policy grants global Culture points that may be spent on social policies. The higher the excess Happiness of an empire, the more effective this social policy is. Small empires that aim for a culture victory might focus on gaining as much excess happiness as possible, creating many Golden Ages in the process. For example, it is possible to have over 60 excess happiness, resulting in over 30
Culture from this social policy alone. However, large empires that spend their happiness on maintaining order in their numerous cities will see little benefit from this social policy.
Theocracy
Temples increase a city's
gold output by 10%.Requires: Organized Religion
As players that choose Piety are expected to build temples in all cities, it is safe to say that Theocracy basically increases the gold output of all cities by 10%. Note that this bonus does not apply to trade route income, which might make a large portion of the empire's gold output. Players of Egypt and Songhai that aim for a large puppet empires will be especially blessed by this policy, as the "commerce governors" of puppet cities always prioritize civilization-specific buildings.
Reformation
Culture increased by 33% in all cities which have built a World Wonder and the empire immediately enters a 
Golden AgeRequires: Organized Religion
Selecting this social policy will immediately start a Golden Age of a standard duration (10 turns on standard game speed), as well as providing a 33% culture bonus in all cities that produced a World Wonder. Effects of this social policy stack with Sistine Chapel (+25% culture in all cities) and Broadcast Tower (+33% culture in city) for a total of a +91% bonus on culture (or +141% with hermitage). For Culture Victories, this social policy is pretty much mandatory. Players with low-production cities are encouraged to create and use Great Engineers for wonder-rushing.
Religious Tolerance
Reduces the Culture cost of future policies by 10%.Requires: Mandate of Heaven, Reformation
Like Reformation, it is also a key policy for Culture Victories and works nice in long term. Note that the effects of this stack with the Cristo Redentor World Wonder.
Finisher
Adopting all policies in the Piety tree will provide a 20% discount on all purchases of religious units and buildings with Faith and Holy Sites provide +3 Gold and +3 Culture.While some of the last policies provide cultural boosts, the finisher turns back to faith. Since you will get much faith from other policies in Piety tree, utilizing them could be very important. With the 20% discount, you can purchase useful things like Missionaries and Cathedrals more easily. Furthermore, it has synergy with the previous faith policies because faith buying the third and fourth Great Prophets is now much more profitable: each Holy Site could now provide a nice gold and culture bonus. The culture bonus matches the main idea of adopting the Piety tree, while gold bonus somewhat makes up a weakness of Piety since there are few gold boosts from other policies in this tree.
General Use
Since choosing Piety basically prevents the player from picking up Rationalism, the Piety social policy tree could probably slow down Science, Diplomacy and Domination victories but it is the key branch for Culture Victories.If you pick Piety, staying small and focused is generally suggested, since Mandate of Heaven, Reformation and Religious Tolerance work extremely well with a tall empire. Obviously, the tree is almost built solely for a Culture Victory. However, the main weakness of Piety is that although the whole tree provides both faith and culture bonuses but they don't work well together. The whole tree seems rather split between faith and culture. The main idea of Piety is actually, first get faith to ensure an early religion, that may provide a culture bonus, and then turn focused on culture. We can consider that the faith bonus finally serves culture. Additionally, the saved production from faith buildings could be turned into Monuments and Amphitheaters.
Normally, the first policy is Organized Religion, since it will be a bit embarrassing if you don't found a religion when you are pursuing for Culture Victory. Also, Organized Religion increases the value of the halved production cost of faith buildings. After Organized Religion, Mandate of Heaven and Reformation will be available and they are equally good (you can actually defer Theocracy until you are ready to finish the Piety policy tree). If you could manage to get wonders in two of your cities or plan to do so right away, pick Reformation. Otherwise build up happiness buildings and adopt Mandate of Heaven. After that, the fourth policy should be Religious Tolerance, which provide a nice discount for all future policies, and finish up Piety with Theocracy.
Synergies with other social policies
Piety works well with the following social policies:a. Aristocracy and Legalism and the Tradition social policy tree in general, as Piety favors strong cities filled with wonders and buildings.
b. Freedom, since players who pick Piety usually head for a Culture Victory. Furthermore, Freedom allows you to purchase Great Artists with faith, which is an excellent way to utilize the extra faith from Piety. Freedom and Piety are the two key branches for a Culture Victory.
Note: Amended from vanilla Piety by Bibor, this article is in G&K version.