The most significant modification in Common Sense is the new provincial development system. Building space in a province is now limited by its terrain and development value. The more developed a province is, the greater wealth and power you can squeeze out of it. By spending monarch points, you can now customize your trading hubs or make great recruiting centers. Fewer, more powerful buildings means that every decision about construction has greater importance – if you want a manufactory and have no building slots in Champagne, what will you destroy?
- Theocracies now have heirs that are chosen by event, with each choice having a different effect and unlocking certain events that can happen once that heir becomes monarch.
- Theocracies now have devotion, which is similar to legitimacy and republican tradition. Devotion goes up from high stability and pious acts and goes down from low stability and low religious unity. Devotion affects your papal influence, church power, prestige and tax income.
- Constitutional monarchy, constitutional republic and English monarchy now have parliaments. Countries with parliaments have to grant a certain number of their provinces seats in parliament, which then allows those seats to vote on issues. The country with the parliament can choose between a few randomly picked issues, and then have a number of years to secure enough votes for the issue to go through. Votes are secured either through events or by bribing parliament seats with things which that particular province wants. After five years of an issue being debated, there is a random chance that the vote will go through at the end of each month, with the chance of winning the vote depending on how many seats are backing it. If the vote goes through, the country gets the benefits of that issue for 10 years, otherwise it suffers a penalty to prestige.
- Protestantism now has church power. Church power accumulates over time and can be used to buy aspects, which are permanent modifiers added to that country's particular version of Protestantism. A country can only have 3 aspects, after which church power can be used to trade in an existing aspect for a new one.
- The diplomatic action remove electorate is now available to the emperor, to remove an elector at the expense of worsened relations with other electors and 10 IA. This action is not available unless the HRE has an official religion. The revoke electorate casus belli is disabled, since this action does the same thing without war.
- Implemented government ranks feature. Each government type can now have up to 3 ranks, with higher ranks conferring better bonuses, and higher government ranks lowering cooldown on changing your national focus. Players with the Common sense expansion can dynamically change their government rank through the government screen and various events and decisions while those without are locked to rank 1 or 2 depending on whether they are independent, unless they are playing or forming a historical empire such as Byzantium and Ming.
- Buddhists now have karma. Karma decreases from aggressive conquest and increases from honoring alliances and releasing nations. Rulers with too high karma become detached from the world and suffer a penalty to diplomatic reputation, while rulers with too low karma will lose the trust of their mind and get a penalty to discipline. Rulers with balanced karma get a bonus to both discipline and diplomatic reputation.
- Can now return an owned province to another existing nation that has a core on it for an opinion boost, at the cost of 10 prestige. Doing so will remove your own cores and claims on the province. This cannot be done while at war.
- The emperor can now grant free city status to nations in the HRE that only own one province. Free cities get a special republican government, a bonus to tax income and will always be able to call in the emperor when they are attacked, even in internal HRE wars. The emperor gets a bonus to tax income, manpower and imperial authority for each free city in the HRE, but there can only be 7 free cities in total at any given time. A free city that gains a second province or leaves the HRE will lose their free city status. Free cities cannot be electors.
- Can now pause westernisation. While it is paused, no monarch power will be spent towards westernisation progress and no westernisation events will fire, but the country will continue to experience unrest.
- Added subject interactions for all subject types. These are special actions and toggles you can enact on your subjects, such as forcing a colonial nation to declare war on another colony, placating a vassal to lower their liberty desire or forcing a lesser union partner to adopt your culture. Subject interactions are accessed through the country subjects screen.
- You can now increase the base tax, base production and base manpower of your provinces at the cost of admin, diplomatic and military power respectively. Cost of developing a province depends on the terrain, the climate, and how many times the province has previously been developed. Certain ideas and modifiers will also increase or decrease development cost. For those without the expansion, reduced development cost ideas will instead give other beneficial effects.
- If you have money to burn, you can now dismiss an advisor from the pool, allowing greater control of the advisors you can select.
- Numerous new events for Buddhists, Protestants, theocracies, the Papal State, subject interactions and parliaments.
- National focus is now also available for players with the Common Sense expansion, even if they do not own Res Publica.
- Added 25 new achievements.
- Added Tengri and Zoroastrian religions.
- Split Buddhism into the Theravada, Mahayana and Vajrayana religions.
- Major update to missions, where many missions were reworked and some pointless and impossible ones were removed. Most missions should now give much more interesting rewards.
- Fort system was completely reworked. Most provinces no longer have forts and unfortified provinces will fall after a single siege phase. Forts are now expensive buildings that cost monthly maintenance, but now have a zone of control in your adjacent provinces that will block the passage of hostile troops and automatically recapture provinces taken by the enemy. You can mothball forts to reduce their maintenance, and your capital always has an extra fort level that costs no maintenance but also does not have a zone of control (unless there is also a fort building there).
- Building system was completely reworked. The number of buildings in the game were reduced and their cost increased, but all buildings should now have a significant effect on their province. Monarch power cost for buildings was removed, but the number of buildings you can build in each province is now restricted by the province's building slots, based on its total development level and terrain.
- Provinces now measure their economic power in development instead of base tax. Development is a combination of base tax (tax income), base production (production income & trade value) and base manpower (manpower).
- Looting was reworked. Provinces now have a 'loot bar' that goes down while regiments hostile to the owner are present in the province. Each regiment loots a certain amount per month depending on their type (cavalry loots the most, artillery the least) and this money is added directly to the looting country's treasury. The province will suffer penalties that get worse the more depleted its loot bar is, and once fully depleted, cannot be looted any further. Provinces that have not been looted for the last 6 months will begin to recover their loot bar.
- Major update to the peace system:
- annex option removed. To annex, you now have to select all of the target’s provinces;
- it is now possible to demand any province from the enemy war leader. Demanding unoccupied provinces cost +10% and capitals +20% war score. Demanding provinces from others work as before;
- revoking cores no longer cost diplomatic power;
- you can now demand gold from a country you are annexing;
- can now use "humiliate" peace option even if you're also taking other things from your rival, but it costs more.
- Numerous bug fixes and updates to peace interface.
- Added Time of Troubles disaster.
- Added English Civil War disaster.
- Added French Wars of Religion disaster.
- Added French Revolution disaster.
- Added Castilian Civil War disaster.
- Added 10 Spanish flavour events.
A list of the dev diaries for Common sense can be found here.