Unless you are a Wizard, chances are Intelligence is going to be a prime candidate for one of your character’s dump stats. In previous editions of D&D, intelligence provided more bonuses than just a modifier to your knowledges and educational background. Another problem with this is there is often a large separation between player knowledge and character knowledge which can often lead to either over or, most-likely, under use of Intelligence checks in general. Here are some ways you can make intelligence less of a universal dump stat.
Grant Bonus Languages
For every positive even-number modifier of your Intelligence score (+2 and +4 / 14 and 18), you can select 1 standard language and learn to read, write, and speak it. If your character already knows every standard language, then they can learn an exotic language.
Grant Bonus Skill Proficiencies
For every positive odd-numbered modifier of your Intelligence score (+1, +3, and +5 / 12, 16, and 20), you can select 1 additional class skill to gain proficiency with. If you are already proficient in all of your class skills, then select 1 skill and gain expertise with it. Standard expertise rules apply.
Make Investigation More Important
If you are running a dungeon crawl or mystery session, read up on the Investigation skill and other Intelligence checks and incorporate them more into your setting. Locating clues to help solve the mystery, deducing that the suicide note found on a desk is a forgery, or figuring out ways the environment can be used against a group of monsters is a great way to help your players think outside of the hack and slash box.
Make Low Intelligence Matter
In 5e, knowing any language allows you to read, write, and speak it. However, this does not mean you are a fluent speaker of the language. This option will add some RP flair to your game. If a character has an Intelligence of 8 or less, their ability to effectively communicate in their languages aside from their race’s own should diminish. For example, while an Orc Barbarian with an Intelligence of 6 is capable of communicating in Orc and Common, their Orc linguistic skills are far greater than their Common skills, so they can communicate normally in Orc but only communicate basic ideas or sentence fragments in Common.
This can have a great impact on how NPC’s react to certain players. Since the player will come off as a baffoon, the NPCs might not take them seriously or outright treat them in unfriendly and unhelpful ways. Just imagine how the average American reacts to someone who isn’t a native English speaker: they laugh or might even insult the person.
Make Proficiency Matter
I will discuss this concept more in a future article, but this issue is paramount when it comes to Intelligence. Characters who are not trained experts in a subject, be it Arcana, History, Nature, or Religion, should not know more than someone who is trained in said subject. With that said, if a character wants to make a knowledge-specific check, they should be required to have proficiency to make the check. Characters can still make general knowledge checks using their intelligence, but anything that falls into one of the 4 main subjects should require proficiency.
If you do not wish to make proficiency a requirement, you should at a minimum give unproficient characters disadvantage on these checks. Bards and other classes that gain a class feature like Jack of All Trades should be treated as being proficient in these skills since they are adding their proficiency bonus, albeit only half of it, to these rolls.