Idea groups guide

This page is a practical guide. For complete description of Idea groups, see Idea groups.

The guide is complete, but it might require further corrections and formatting.

While the idea groups themselves are mostly self-descriptive, understanding their benefits and situational usefullness might still pose a challenge to some players, especially beginners. The purpose of this guide is to help them choose which ideas are the most suited for their situation.

Important notes

In order to remain short and effective, this guide doesn't include complete and precise enumeration of each group's bonuses - for that, see Idea groups. It assumes the reader already knows what each idea group offers, but is unsure how exactly can they benefit them.

This guide is based on analysis as well as on personal experience. Different players may therefore have different recommendations and highlight different things they consider important. It is in no way dogmatic and readers may devise new and more optimal uses of idea groups themselves as well.

Recommendations of individual idea groups do not cover achievements.

Situational analysis

It is recommended to analyse your current situation first, even before the opportunity to pick a new Idea group presents itself. There are two main factors one should consider:

Player's goals and ambitions

I.E. what do you want to achieve? Conquer the world? Restore the Holy Roman Empire? Create a colonial empire and amass riches? Go for a specific achievement? Even with smaller, simpler goals, like playing historically or unifying home region, it's always helpful to think about what would help you reach them.

Player's current situation

It's usually worth to check the situation your country and its surroundings is currently in.

• Your country's National ideas. Aligning one's new Idea groups with National ideas usually serves one of two purposes - to create a balance and cover the country's weak sides, or to combine the bonuses to reach even a higher peak. For example, Prussia is famous for its effective army, but it might need boosts to its economy to support it. Meanwhile Austria already has decent national ideas for diplomacy, yet players still take diplomatic ideas to further strengthen their position as Holy Roman Emperor.
• Your geopolitical situation. Higher developed provinces, like in Western Europe, mean stronger economy, but also higher aggresive expansion impact. Having large amounts of terrain that is easy to develop (farmlands, grasslands etc.) might encourage "tall gameplay", while mountains and deserts probably won't. Neighbouring heretics or heathens offers a chance to go for a holy war, but that leads to increased revolt risk and possibly expensive converting. Distance to the New World means that for example Holland or Denmark can't start colonising as soon as Portugal and Spain, forcing them to stay in their continent longer.
• Monarch power points avaible. Abundance or, on the other hand, lack of admin, diplomatic or military points may be an influental factor for (not) choosing an idea group from the corresponding category. Having a (4/5/1) ruler means the player won't have too many military points to spend, therefore taking military idea group might be discouraged. Other strains on monarch points include annexing provinces, integrating vassals, barraging enemy forts, lack of decent advisors, getting behind in technology or previously taken, unfinished idea groups.

Administrative idea groups

Economic

Economic idea group is one of the most self-explanatory: All its ideas focus on improving country's income and reducing expenses. Increased province income, cheaper construction and reduced development cost helps player to get maximum from the provinces they already own, while making sure to minimise the losses from local autonomy. Reduction of inflation and yearly interest mitigates the negative effects from taking money in a peace deals, taking loans and relying on gold mines.

Recommended for/when:

• For overall increase of player's income.
• If you plan to "play tall" (Strategy based on improving one's own provinces rather than making vast expansions.)

Innovative

Innovative ideas are in way similar to economic, but they don't focus solely on money. Institution spread bonus and reduced embracement cost, combined with reduced technology cost allow player to stay up-to-date with technology without spending that many ducats and monarch points. Reduced advisor cost means being able to afford high-tier advisors earlier (or to save the money instead). Rest of the ideas have similar effect - reducing the need to spend monarch points or lowering the cost.

The strongest side of Innovative ideas is their all-round usefulness. Practically all coutries and strategies include unlocking technologies and institutions, thus they can greatly benefit from these improvements. The weakest point is that in order to fully unlock their potential, they should be taken among the first idea groups, and these slots are usually reserved for more important ones. Some countries (and associated strategies) require to rush military ideas for survival, religious ideas for dealing with different religions and exploration + expansion for colonial powers. To improve the economy, players also usually rather go for economic or trade ideas instead. It is, however, still viable to take this idea group later, should you wish to.

Recommended for/when:

• If you want to generally improve your country, while not feeling pressed to focus on more important matters like colonisation, military and internal stability.

Religious

Both religious and humanist ideas help deal with the issues that come with expanding into land with different religions and cultures, namely unrest caused by separatism and intolerance penalties. The first group represents the "strict" way, ensuring stability by maintaining religious unity. One extra missionary, combined with increased missionary strength and reduced maintenance cost greatly help with converting provinces, while increased tolerance of the true faith helps to keep new converts from revolting. Reduced culture conversion cost makes it easier to convert new provinces to one of your accepted cultures, completely eliminating intolerance penalties. It also offers bonuses to specific mechanics, like papal influence for catholic countries or patriarchal authority for orthodox ones.

The most notable aspect of religious ideas, though, is the "holy war" casus belli. It's a permanent justification for war against every neighbouring heretic and heathen, allowing to take every province (without spending diplomatic points, if you have no claim) and with only 75 % aggresive expansion. It's not uncommon to take religious ideas for the casus belli only, paying little attention to actual converting. (For example, muslim countries with access to dhimmi estate can completely negate heathens' effect on religious unity by giving them specific rights.) Holy war usually loses its importance later, once "imperialism" CB becomes avaible.

Recommended for/when:

• When you plan to rapidly expand into heretic and heathen countries, and/or:
• If you want to maintain religious purity (for example in the HRE).
• If you need better casus belli for rapid expansion.
• If your religion, government mechanics and/or national ideas offer significant bonuses to provinces with true faith. (Orthodox patriarchal authority is a perfect example. In combination with national ideas and mission trees, it makes religious ideas a perfect choice for Byzantium or Muscovy.)

Humanist

While religious ideas choose the "strength in unity" approach, humanist idea group is for those who opt for "strenght in diversity". Religious unity bonus, increased tolerance of heretics and heathens, combined with reduced years of separatism and national unrest mean that the people will have little to no reason to revolt, even without being converted to the true faith. Increased limit of accepted cultures further reduces the need to convert them. Reduced idea cost is also a great reward for taking humanist ideas early.

The greatest downside of humanist ideas is the absence of the "holy war" CB which comes with religious. This is partially compensated with a +30% bonus to improve relations, that makes aggresive expansion wear off faster and helps calm down outraged countries.

Even though religious and humanist ideas look mutually exclusive, there is no problem taking both. For example, taking religious first for the CB and humanist later for dealing with rebels is a viable strategy.

Recommended for/when:

• When you plan to rapidly expand into heretic and heathen countries, and/or:
• When you don't need/want to spread your country's true faith.
• When you don't need the "holy war" CB from religious ideas. (For example, "imperialism" is already enabled.)
• If you play as a horde. (Hordes have their own special CB, they have usually weaker economies and with them players usually expand too fast for missionaries to catch up.)

Administrative

Administrative ideas can be divided into two main groups. The first one consists of three ideas that focus on mercenaries - cheaper hiring, maintenance and higher manpower. The second group helps create and maintain vast empire. -25 % Core creation cost allows cheaper integration of newly conquered land and creating states, while the group's bonus, government capacity, greatly increases their limit, reducing the need to rely on relevant estate privileges, large and powerful subjects and/or suffering the penalties. 10 % discount on administrative technology also easies player's strain on admin points.

Recommended for/when:

• When you want to expand rapidly, or even going for world conquest.
• When you struggle with government capacity, either because of your country being too vast, or due to gov. cap. maluses. (Like for example Prussia.)
• When you rely on mercenaries. (Commonly done to save country's own manpower.)

Expansion

This idea group has two focal points: creating a vast colonial empire and bringing the generated wealth back home. 2 Extra colonists, together with global settler increase and increased settler chance means fast colonising, and one extra merchant, increased global trade power and reduced cost of upgrading trade centers means easier time steering trade from overseas back to player's main trade node. The only downside is the absence of ability to explore the unknown land, making expansion ideas a common follow-up for exploration ideas. Extra diplomatic relation slot is not needed for this, since colonies and trade companies require no "upkeep", but it's a nice bonus for creating new alliances both home and in the colonial regions. Reduced minimum authority in territories means that (without any other bonuses of the same type) the income from territorial provinces doubles. It's still only 2/10 of fully stated provinces, but the more territories the country has, the more significant the difference becomes.

Recommended for/when:

• For aspiring colonial powers
• For expansion into nearby uncolonised provinces. (Like in Africa, Indonesia or for New World natives.)
• For creating "land bridges", like from Kongo region to Rwanda and/or Mutapa.

Diplomatic idea groups

Exploration

Exploration idea group is a fittingly sorted starter pack for any aspiring colonial power. It grants the ability to hire explorers and conquistadors as soon as you unlock the first idea, followed by a colonist granted by the second one; allowing immediate colonisation of new lands.

However, it's greatly recommended to consider the biggest limiting factor to colonisation (aside from the speed of colonial growth): colonial range. Third idea from this group grants +50 % range, however, due to distance to the New World, some aspiring colonial powers might need to acquire further bonuses (like from advisors) or to get a foothold closer to desired lands in order to reach it. (For example, England might annex irish minors to get closer to North America.) Higher levels of diplomatic technology also increase the colonial range (with level 7 being the first notable threshold), however, longer waiting probably means that large portions of colonisable land will already be taken by more determined and better positioned colonial powers, traditionally Castile and Portugal.

Exploration idea group may also be used for mapping of enemies' overseas holdings in order to take them in peace deals, or for finding a way through uncolonised terrain (+ creating a land bridge), like from Kongo to East Africa and vice versa. For these purposes, it's common to just unlock the first (and the second) idea and abandon the group once the task is completed.

Recommended for/when:

• For exploring the unknown lands.
• For starting and expanding a colonial empire. (Can be followed by expansion ideas to increase the speed and scale.)

Diplomatic

Diplomatic ideas are a perfect choice for influencing foreign countries, bending them to one's will and staying on good terms with them. Two extra diplomats, combined with increased diplomatic reputation, improve relations bonus modifier and one extra diplomatic relation slot greatly enhance player's diplomatic flexibility; they will have easier time befriending other countries, convincing them to do their bidding, appeasing them when outraged and creating larger alliance and subject networks. This is further enhanced by group's bonus, "Lowered impact on stability from diplomatic actions", making penalties from actions like breaking royal ties and attacking without proper CB far more bearable.

Reduced diplomatic technology cost also reduces player's demand for diplomatic points, leaving more for actual diplomacy (or country development, for example).

Special attention goes for -20 % province warscore cost modifier, which allows taking far more land in a peace deal. This makes diplomatic idea group a great tool for creating vast empires, or even conquering the World; considering that the rest of the group help with potential coalitions from excess aggresive expansion.

Recommended for/when:

• If you want to stay on good terms with AI countries and make them tolerate your excesses (Aggresive expansion, breaking promises, etc.)
• For rapid expansion, or even World conquest.
• For creating large alliance networks.
• For attempting to get personal unions. (Cancelling royal ties once it's certain you won't get the union no longer costs stability.)
• If you want to be the emperor of HRE.

Influence

Influence ideas are in a way similar to diplomatic, however their main targets are not player's allies, it's rather their subjects. While some bonuses affect only vassals, like increased tax and land force limit contribution, all subjects are affected by -15 % liberty desire, effectively keeping large vassal swarms, strong personal union partners and colonies in check. Once the time comes to annex some of them, the suzerain gets a 15% discount on diplomatic points. Diplomatic reputation bonus and an extra diplomatic relation slot, the same bonuses diplomatic group offers, also help creating large network of vassals and speed up the process of annexation, but they're useful in broader diplomacy as well.

The idea group's bonus reduces the diplomatic points cost for unjustified demands in a peace deals, like unclaimed provinces in a "conquest" war, to half.

The main downside of this idea group is that it offers no diplomats. The player will have to either rely on their own or to get them elsewhere, like in other idea groups and their corresponding policies.

Recommended for/when:

• If you have strong subjects of any type, colonies included.
• If you plan to expand using subjects. (Diplo-vassalising/releasing a weakened country and then re-conquer their cores; or just giving your subject land to core and then annex them to save administrative points and reduce overextension.)

Espionage

Like diplomatic and influence, espionage idea group also helps with expanding and influencing other countries, but it takes somewhat less direct approach. Building spy networks is faster and the cost of fabricating claims is reduced. This, combined with one extra diplomat, allows rapid justification for wars of conquest. The wars themselves will be slightly easier due to +10% siege ability, just like post-war recovery thanks to -0.10 yearly corruption.

Probably the most notable bonus is -20% aggresive expansion modifier, effectively preventing possible coalition by simply not giving them a good enough reason to join. This can be invaluable in regions where aggresive expansion can be a serious issue, like in the HRE, or just Western Europe in general.

Espionage ideas are somewhat unpopular among EU4 player community; even though the bonuses are solid, they are missing on actual usefulness. Time difference in claiming just one province (enough to get a CB) with/without expionage ideas is not that large and other covert actions tend to have little effect. Supporting rebels to create a separate country or to force a religious convertion sounds like a fun alternative to waging wars, however, it costs vast amounts of ducats and many of the target countries can still deal with supported rebels easily. This doesn't mean, however, that the idea group is useless, it's just more situational.

Recommended for/when:

• For rapid expansion into areas with the same religions.
• For countries which get little to no claims from their mission trees.
• For overally reducing the aggresive expansion impact.

Trade

Trade ideas are, along with Economic, one of the best ways of improving player's income. The idea group's base consists of three(!) extra merchants, which can be assigned to steer and collect trade that would otherwise be wasted. This is paired perfectly with other bonuses, which allow player to reach further trade nodes, steer trade from them more effectively and then generate higher actual income when collecting it.

Trade is a rather complex mechanic of EU4 that can be challenging to grasp, but for the purpose of this guide it has to be reduced only to few universal rules. Generally, players might want to take trade ideas if they have access to far more trade nodes to steer from than they have merchants. Great example are the countries situated in Indochina or Malaya trade regions: while they have access to multiple upstream trade nodes in East Indies and China superregions, they still only have 2-3 merchants, thus a lot of their trade power is wasted. Countries on the same superregions can't be assigned to trade companies, eliminating another solid source of merchants. On the contrary, Trade ideas are almost useless for regions with no trade nodes to steer from, like Tibet, Western Africa, Peru or Far East (before colonising North America).

Main difference between Trade and Economic ideas is that Trade ones offer no bonus for playing tall - actually, they benefit more from expansion. Generally expanding into upstream trade regions, or just undertaking surgical strikes for provinces with high trade value, (and possibly creating trade companies there) goes well together with this idea group, allowing effective tapping into trade networks further away.

Recommended for/when:

• For overall increase of player's income. (While not playing tall; otherwise Economic ideas are preferred. Though, both groups can be taken as well, they are not mutually exclusive.)
• If you have access to multiple lucrative trade nodes, but are limited by the number of merchants. (I.e. no colonies and no trade companies strong enough to get associated bonuses.)

Maritime

Maritime ideas are meant to strengthen the player's navy, mainly from quantitative and economic perspective. Ships will be cheaper to build, their force limit will be higher, they'll require fewer sailors for maintenance and will be repaired faster when needed. Ships' effectivity is also increased - privateering, blockading and trade protection will require fewer ships to do the same amount of work. While increasing the player's amount of sailors, it also gives access to Marines (With Rule Brittania or Golden Century DLCs) - special units meant for amphibious assaults. One extra leader without upkeep and -25% admiral cost also help player conserve precious power points.

Maritime group's bonus include +1 fleet movement speed and the ability of ships to repair in coastal sea zones. While not being too important, these bonuses can be highly convenient, for it means easier catching of enemy fleets, less time spent on open sea (and therefore less attrition, especially for units being transported) and reduced need for ships to stay in harbour for repairs.

It might be worth pointing out that maritime ideas are some of the least popular in the game, probably due to the game's focus on land combat. Even though naval superiority is usually helpful, wars are ultimately decided in land battles. For example, even if Castile completely blockaded France, they still lose the war if France wins land battles and occupies their provinces. Even in amphibious assaults, naval supremacy is just the first step, after which the attacker needs to occupy the land. This doesn't mean that Maritime ideas are useless and that players are meant to be discouraged from taking them, but that these ideas are highly situational. It's recommended to have the land secured first and then increase naval efforts.

Recommended for/when:

• If you play as a pirate republic.
• For island countries, or for those who rely on transporting troops between different islands (and/or mainland).
• If you've been landlocked most of the game and now you need to catch up with more maritime-focused enemies.

Military idea groups

Defensive

Defensive ideas encourage specific playstyle, militarily speaking - working with terrain. Forts are cheaper and can hold on for longer. This, together with +1 Land leader maneuver, helps fighting on a favourable terrain as a defender, transfering penalties to your opponent's army instead. Armies themselves are also further strengthened with +15% morale and increased military tradition from battles. This idea group also reduces attrition damage for your troops, while making your opponent suffer exactly the opposite on your territory. It also boosts your reinforce speed, allowing to replace losses and get your armies back to full strength faster.

Defensive ideas are considered one of the weakest in the category, probably due to their difficulty to be used effectively. Besides choosing favourable terrain they offer almost nothing to battles themselves - notably only morale, which becomes less significant as the game progresses. Relying on defense also means taking less direct approach, prolonging wars to drain opponent's manpower rather than winning battles. If your main concerns are winning battles or maintaining manpower, taking offensive, quality or quantity can be a better idea.

This, however, doesn't mean the idea group is useless. If your geographical situation shows potential for highly defensible chokepoints, having forts there improved by defensive ideas can create tough barrier, either securing your border and/or distracting opponents while focusing on other military operations. Attrition, while not being the most decisive factors, can be deadly in some regions, like in those with severe winters, deserts or tropical lands with monsoons.

Recommended for/when:

• When your country's terrain offers great defensive possibilities.
• If you prefer playing defensively.

Offensive

Offensive ideas help player get together a powerful army for both battles and sieges. +1 Land leader shock and fire means your armies will get better leadership, and together with +5% discipline this greatly increases their effectivity in battles. Sieges are also made faster with +20% siege ability. Other ideas in the group help with maintaining larger armies, getting more prestige, recruiting regiments faster and with army morale recovery, so they restore their lost morale faster.

Recommended for/when:

• If you are usually on the offense.
• If you need to overally strengthen your armies.
• If you struggle to get decent generals.

Quantity

Quantity idea group is quite self-descriptive. Land force limit greatly increased, together with regiments being cheaper to recruit and maintain, allows for much larger armies. But probably the main thing is having enough manpower, as frequent battles, sieges and marching through environmentally hostile terrain can quickly drain one's reserves. +50% National manpower modifier together with +20% recovery speed greatly improves players' reserves, while bonuses to national supply limit modifier and land attrition prevents unnecessary losses due to movement and sieges in hostile terrain. One of the ideas also increase player's garrison size, meaning enemies will have to bring more troops to siege your forts.

Unlike other idea groups, quantity offers no army improvements except for quantity itself. This can be useful if the player can combine it with other idea groups/their national ideas, when managing large empires (allowing to have enough units on all fronts) or when they're sure they can simply overwhelm their opponents. Otherwise, they may find out they have much difficulty actually winning battles, even with bigger numbers.

With Leviathan DLC, players may as well spend extra manpower on speeding up the construction of monuments, making manpower even more valuable.

Recommended for/when:

• When you need much more manpower.
• If you prefer having a large army instead of smaller, highly capable force.
• If you need more troops to fight in many different areas at once.
• If you want to play tall. (Quantity ideas greatly help with getting maximum manpower from your provinces and buildings.)

Quality

Quality ideas are the direct opposite to quantity - instead of providing extra troops and manpower, they greatly increase effectivity of the army player already has. +10% Combat ability for all land units ( infantry, cavalry and artillery), together with +5% discipline improve the army's performance in battles. Increased army tradition also means more capable armies, as well as higher chance to get decent leaders. The rest of the ideas is dedicated to improve player's navy - this is excellent for improving naval force without dedicating an entire idea group to it, but if naval battles have little to no importance to the player, these ideas are wasted.

This idea group, together with quantity (see above), often raise a question which approach is better. Both have their strengths and weaknesses and they can reach similar effectivity - quality decrease one's losses, while quantity allows their easier replacement - so, in the end, it's down to personal preferences. Though, just like with any other idea groups, they are not mutually exclusive and it's completely viable to take both groups in one campaign.

Recommended for/when:

• If you need to improve your standing armies.
• If you prefer having a smaller "task force" instead of large, weak armies.
• If you want to improve your navies.
• If you need to improve your armies, but don't need/can't afford more troops.

Naval

Naval ideas are all centered around player's navy, but unlike maritime ideas, they focus on its military side. Player's fleets will become more durable, better moralised and led by capable leaders, significantly increasing chances of winning battles and ships surviving it. On top of that, heavy ships and galleys acquire their own improvements in combat ability, helping both inland (Like Venice) and oceanic maritime powers (like Castile). The idea group also increases sailor recovery speed, which is important for building and maintaining fleets, and gives access to marines, special land units adapted for amphibious military operations.

Despite naval ideas being strong, this group is probably the least popular one in EU4. Just like with maritime ideas (see above), the problem is probably the game's focus on land battles, and even though naval dominance and blockades can give winner large amounts of war score, ultimately, wars are decided on land. This makes naval ideas highly situational, as they reach their maximum effectivity only when you can separate your lands/the war goal from enemies or when you want to stop someone who tries to do that.

Recommended for/when:

• If you need to improve the war capabilities of your navy.
• If you can use navy as a wooden shield, or for defeating someone who does (like Great Britain).
• If you play as a pirate republic.

Government-based idea groups

Include Aristocratic, Plutocratic, Horde, Divine and Indigenous.

These idea groups are, sort of, a special subcategory within military idea groups. What makes them unique is the fact that the player has access only to one of these, based on their government form (and/or reforms). Despite this fact, none of these are mutually exclusive: if the player unlocks one of these groups and then changes government, they can unlock the new group without losing the old one.

Despite each group contains unique bonuses, they share enough similarities to be able to be summarised with one general description. All of these groups don't focus entirely on improving the player's military, but they also offer various different bonuses that improve and encourage style of play that is commonly associated with these government forms. Due to this, descriptions of individual groups will be brief and recommendations general, shared by all groups.

Aristocratic ideas are for monarchies and tribes. They offer, aside from military bonuses, extra diplomat and reduced military technology cost. +10% Nobility loyalty equilibrium also helps keeping the referred estate in check.

Plutocratic ideas improve republic and plutocratic-like monarchies. Aside from military, they offer several bonuses for trade, including one merchant. They also help maintaining country's stability, with -2 national unrest and +10% burghers loyalty equilibrium.

Divine ideas are accessible to classic and feudal theocracies. They focus mainly on religious expansion, offering discount for enforcing religion and culture conversion, while also incresing internal stability with -2 national unrest and +10% clergy loyalty equilibrium. While they seem like an alternative to Religious ideas, their bonuses are almost completely different, except for clergy loyalty equilibrium and culture conversion cost, which stack perfectly.

Horde ideas are, as the name suggests, meant for steppe nomads. While they offer little military bonuses, except for significant cavalry improvements, they greatly help with massive expansion, which is a common playstyle for hordes. -10% Aggresive expansion impact prevents some coalitions. +2 Promoted cultures, +25% religious unity and -1 national unrest helps against rebels. +20% Trade steering improves country's trade income.

Indigenous ideas are meant for primitive tribes in the New World. Aside from mediocre military bonuses, they help tribes achieve what they usually need - to develop, reform their government and catch up with the colonisers technologically.

Recommended for/when:

• If you want to improve your military, but also need several other improvements, while having only one idea group slot avaible.
• If you're not sure which military idea group to take, and/or want to try something alternative.
• (For Aristocratic and Horde) If you want to focus on cavalry.

Examples

Here are some practical examples of decision-making readers may take inspiration from. Remember that it shows only one of the ways these countries can be played, not the only one possible at all.

Castile: Due to its mission tree and perfect geographical predispositions, the player decides to start with exploration and then expansion ideas to start a colonial empire. As a third group, they'd like a military one, not to fall behind - and they go for quality, as it improves the navy as well, which is essential for Castile's success. After some time colonising and following their mission tree, player finds themselves with several powerful subjects, so they choose influence ideas to keep them in check. They might as well go for , since colonising creates a lot of heathen neighbours and they want to invade North Africa anyway to stop them from raiding their coasts. After that point, choices of idea groups become far more open; the player might take another military group to strengthen their army, trade to get even higher income from all the accessed trade nodes, or diplomatic to become the HRE emperor in order to complete spanish mission tree and get the achievement.

Byzantium: After winning the initial war against Ottomans, it's becoming obvious to the player that they'll need three things: more troops (and manpower) to keep waging wars, a way to deal with non-orthodox neighbours (and provinces taken from them) and an economy to be actually able to support it. Quantity is an obvious answer to the first issue. As a second group (can't take it as the first one, since rapid expansion and advancing in administrative technology already mean a severe demand for admin points) they pick religious - in this case it's far superior than humanist, since orthodox countries greatly benefit from provinces with true faith and Byzantium has access to many bonuses to missionary strength. Next they take trade ideas to solve the economy issues, since player's capital, Constantinopolis, can be a powerful trade hub with a lot of trade nodes to steer from. After getting a solid foothold in the region, the player decides to reform the Roman Empire, which means vast territorial expansion. To do that, they decide to continue with diplomatic (for reducing province war score cost and to prevent coalitions), administrative (to create cores more cheaply and to increase governing capacity) and offensive or quality for fighting stronger european countries. Since the player did a mistake of neglecting their navy, they chose to unlock naval ideas in order to catch up with the navy of Great Britain, which they need to defeat to acquire all the provinces needed.

Bohemia: A few years after the game starts, the player is presented two options - both lead to vastly different playstyles. By choosing to convert to hussite, they get an unique religion, finding themselves in the middle of a heretic continent. In that case, going for quantity or offensive and religious sounds like a great start for massive conquests. Staying catholic offers another opportunity - Bohemia is in the perfect position to replace Austria as the HRE emperor. In that case, diplomatic ideas are a necessity to maintain good relations with other electors. Since the emperor gets significant bonuses to manpower and land force limit, quantity ideas are no longer important to player and they may pick quality instead. If they plan to fully reform the HRE, they might still take religious ideas to fight reformation (and other heretics and heathens)

No matter which path the player chooses, Bohemia might also benefit from influence ideas to manage various subjects (from their mission tree) or economic, if they want to play tall. If they aim for "The Bohemians" achievement, which requires owning a province in Ireland, they might as well take maritime and naval, since they spend a lot of time landlocked and their navy may be therefore no match for England/ Great Britain.