Intelligence

Intelligence is one of seven primary statistics in the SPECIAL character system.

Fallout, Fallout 2 and Fallout Tactics
Modifies: the number of new skill points per level, dialogue options, and many skills.

One of the unique qualities of Fallout and Fallout 2 was the difference in gameplay caused by creating a low-Intelligence character. With a dimwitted player character, many non-player characters will simply shrug one off, while others will insult or even attack them. It is possible to complete the game as an idiot, but most side-quests are impossible to do, and character growth is limited, as is the story involvement possible - while it is possible to bumble through the main quests, almost all plot details and background information will be left missing. Furthermore, due to limited-at-best non-player character interaction, almost all side-quests are unavailable. Because of this, playing as a low Intelligence character is only recommended for experienced players looking to role-play, or as a humorous replay option.

Ways to increase Intelligence

 * In Fallout, the Brotherhood of Steel doctor in the Lost Hills can perform an operation to permanently increase Intelligence by 1, assuming it can be afforded.
 * Intelligence can be raised permanently in Fallout 2 in three ways. First, by using ACE and the yellow memory module (+1). Second, by the Hubologist zeta scan/alignment in San Francisco (which can also provide +1 Luck, though the game may need save-scumming to get a bonus rather than a penalty). The paste method is to take the Gain Intelligence Perk. The bonuses from these methods stack for a total of +3 Intelligence.
 * In both Fallout 1 and 2, Mentats can be used to temporarily raise Intelligence by 2.
 * In Fallout 2, Intelligence can be temporarily raised by 1 point by the Purchase the Kesting Special quest given by Miss Kitty in the Cat's Paw brothel.

Fallout 3
Modifies: Medicine, Repair, and Science skills, as well as the number of new skill points per level.

Intelligence determines the number of skill points earned per level up. The base number of skill points gained per level is 10 + INT. Skill points gained for raised Intelligence are not retroactive for past levels, so increasing this primary stat early, if at all, is the best. Also, temporary modifiers to Intelligence (e.g. from Night Person or Button's wig) do not affect the number of skill points gained when leveling up.

Ways to increase Intelligence

 * Permanent
 * Bobblehead - Intelligence (+1)
 * Intense Training perk (+1 per rank)
 * No Weaknesses perk (will raise base to 5 if below 5.)
 * Almost Perfect perk (will raise base to 9 if below 9.)
 * Temporary
 * Button's wig (+1)
 * Lincoln's hat (+1)
 * Berry Mentats (+5)
 * Mentats (+5)
 * Night Person perk (+2 between 6:00 PM and 6:00 AM)

Fallout: New Vegas
Intelligence affects skill points differently from how it did in Fallout 3. The number of skill points gained each level is based on the formula 10 + (0.5 * IN) per level, including level 1, where IN is the Courier's Intelligence. If one gets a non-whole number of skill points per level (e.g. 10.5 for INT 1) it will be saved for the next even level up (see Skill Rate).

Ways to increase Intelligence

 * Permanent
 * Intelligence Implant available at the New Vegas medical clinic (+1)
 * Intense Training perk (+1 per rank)
 * Completing the quest The Apocalypse or The End will allow raising any one primary statistic by 1.
 * Temporary
 * Only permanent increases in Intelligence will increase points received when leveling up. While traits are relatively permanent (they cannot be changed at any time like the other temporary items), they will not increase level-up points.
 * Armor and clothing
 * Mad scientist scrubs, Scientist scrubs, Dr. Klein's glasses (+1)
 * Dr. Klein's scrubs, Dr. Mobius' scrubs, Dr. Mobius' glasses (+2)
 * Chems
 * Mentats (+2)
 * Party Time Mentats (+2)
 * Perks
 * Meat of Champions (+1 for 60 seconds after eating a corpse.)
 * Night Person (+2 between 6:00 PM and 6:00 AM)
 * Traits
 * Claustrophobia (+1 while outdoors, but -1 indoors)
 * Early Bird (+2 between 6am and 12pm, but -1 between 6pm and 6am)
 * Black coffee (+2 - +6 depending on Survival skill)
 * "Smart Light" (+2 for 12 hours or until the player uses the "Mood Lights")

Intelligence in quests and exploration

 * When speaking with Arcade Gannon, a Courier with an Intelligence of 3 or less can convince him to become their companion by stating "This place is really complicated and stuff. You're smart, can you help me do... stuff?"
 * Having a character with Intelligence of 3 or less can grant "special" Intelligence checks. If the character's Intelligence is really low, dialog options will appear to be short and monosyllabic, with barely any sentience.
 * When first meeting Ignacio Rivas at HELIOS One, he will ask the player character what their interest in the place is. If the their Intelligence is high, they may respond with "My interest in this place is scientific." However, with a low Intelligence, the same option will be available as "I is scientistic."
 * An Intelligence of 6 is needed to tell Veronica that the Brotherhood of Steel are only hostile if one uses plasma or laser weaponry around them. Otherwise, a Courier with low intelligence can only humorously state the Brotherhood are known to shoot lasers from their eyes.
 * An Intelligence of 6 is needed to ask Arcade Gannon how he knows so much when one enters REPCONN headquarters.
 * An Intelligence of 6 is needed to ask Orris how he managed to kill 4 thugs with 3 shots during the G.I. Blues quest.
 * To convince Joe Cobb that he can be the newly (self-appointed) mayor of Goodsprings, an intelligence of 6 is required.
 * A Intelligence of 6 is required to tell Boone that snipers work in teams as a dialogue option at the end of One for My Baby.
 * An Intelligence of 6 is needed for Dr. Mobius to reveal that they are still planning how to save themselves.
 * A character with an Intelligence of 6 or lower will admit they don't know what a fish is during a conversation with Cass. With an Intelligence of 7 or higher the Courier will ask Cass in return if she knows it.
 * An Intelligence of 7 or a Speech of 70 allows the Courier to talk Alice Hostetler down from killing her mother in the quest Someone to Watch Over Me.
 * An Intelligence of 8 is needed to trick Silus into thinking the Courier is an agent of Caesar's Legion on a mission to kill him. Silus will take the bluff and inform the Courier about Caesar's brain tumor and indirectly about Ronald Curtis.
 * An Intelligence of 8 is needed to reveal the fact that Dr. Mobius scattered the personality chips across Big MT.
 * An Intelligence of 7 and a subsequent value of 9 or having the Math Wrath Perk is required to resolve 0|Dr. 0's naming issue.
 * During the quest, Come Fly With Me If your Intelligence is below 4, you can also try randomly mashing the buttons on the control panel. Watch the cut scene as the rockets take off from the opened launch hangar. You should see a notification that your reputation in Novac is improved.

Fallout 4
Unlike in previous games, Intelligence has no effect on skills, since Fallout 4 lacks a separate set of scores for your skills. Instead, a higher Intelligence—in addition to unlocking higher perks in the Intelligence category—will increase the amount of experience your character earns from all sources.

The experience multiplier linearly increases from 103% (1 Intelligence) to 130% (10 Intelligence). In other words, it increases XP gains by 3% per INT. It continues increasing if Intelligence is brought higher than 10. In math terms:
 * $${\it XP}_{\rm Final} = {\it XP}_{\rm Base}\times \left(1 + \frac{{\it Intelligence} \times 3}{100}\right)$$

A higher Intelligence also reduces the number of words that are displayed while hacking a terminal; for example, at an Intelligence of 10 or higher with a Science bobblehead, it almost becomes trivial to brute-force most hacking sessions.

Ways to increase Intelligence

 * Permanent
 * Level (+1)
 * Intelligence bobblehead (+1)
 * You're SPECIAL! book (+1)


 * Temporary
 * Armor and clothing
 * Liam's glasses, Lab coat, Press cap, Ushanka hat
 * Legendary armor effects
 * Chems
 * Berry Mentats
 * X-cell
 * Perks
 * Night Person
 * Settlement objects
 * Vault 88 overseer's desk (+1)

Ways to decrease Intelligence

 * Temporary
 * Armor and clothing
 * Chems
 * Daddy-O
 * Dirty Wastelander
 * Beer
 * Settlement objects

Intelligence in quests and exploration

 * The Last Voyage of the U.S.S. Constitution has multiple intelligence checks that can speed up progression through the quest. Instead of replacing components, the player can repair them instead. This strategy applies to the replacement of the wires (requiring an intelligence of 5) and radio antenna (with a score of 9 int).
 * When romancing Magnolia, she may compliment the character's intelligence if the score is his or her highest SPECIAL attribute.

Fallout 1 & 2
When the player character in Fallout and Fallout 2 has less than 4 Intelligence, the biggest change in gameplay is undoubtedly the dialogue. Upon reaching Shady Sands, the villagers take pity on the Vault Dweller, and Aradesh will simply shrug them off. The best they can speak is half-word sentences or gibberish.

The real downside, though, is the nigh impossibility to do about 90% of the side quests. No one will talk to a moron or even give them the time of day.

In Fallout 2, the Chosen One may meet Torr, the "town simpleton of Klamath," who would normally give them a quest to help protect his brahmin against "the evil bugmen." If the player character has low Intelligence, however, he will appear to be highly intelligent as if being stupid has a culture and language of its own. Two flat-headed people can have a complete, thought-provoking, and fully articulated conversation between them.

Another person one may have an "intelligent" conversation with in Fallout 2 is AHS-9, who becomes able to understand what the Chosen One tries to say after the alignment, and gives the quest to kill the Shi Emperor.

When talking to Algernon in the basement of New Reno Arms, the Chosen One can start a childhood "cop and robbers" type dialog in which they accidentally "shoot" and kill him.

A character with a low Intelligence is unable to gamble. When they observe a roulette table or a slot machine, the character will respond to it as a fun toy or an interactive character, respectively. Visiting a craps table will result in a dumb Chosen One commenting to the dealer that they "play craps in pants".

Fallout 3
In Fallout 3, there are conversation situations where characters with low Intelligence are granted other dialog options, often relating to their low intellect. However, these options are few and far between, unlike the other Fallout games where one could play the entire game as a person without Intelligence. One instance is in Roosevelt Academy, where if the Lone Wanderer activates Dean Dewey while having an Intelligence below 4, he will deem them a "special needs" child, and escort them to a "proper room."

Fallout: New Vegas
In addition to alternative Intelligence checks, low Intelligence changes some dialog options when speaking to vendors and non-player characters. For example, when speaking to Miguel at Miguel's Pawn Shop, the option to start trading is "Me buy things," and when speaking with Dr. Usanagi at the New Vegas medical clinic, after she gives the Courier the initial description about implants they get the dialogue option "You sell plants, too?", which will cause her to re-explain the implants and suggest [the player character] take the implant to make them smarter. If taking her up on this deal, she will state that she thinks the Courier "could really benefit from it," and offer the implant at a discount.

In place of the gibberish of past games, however, the player character will simply not completely understand a conversation, confuse what someone is saying with something else entirely, or not understand what situation they are currently in. In the REPCONN headquarters, for example, a character with an IN of < 3 can bypass a robot that demands a password by saying "ICE CREAM!" Normally, a Luck of at least 7 would be needed to guess this.

Low-intelligence characters attempting to do the quest That Lucky Old Sun will be granted several unique and highly entertaining dialog options when conversing with Fantastic and Ignacio Rivas. An example is when informed about the hostilities between the Followers and the NCR, the Courier can ask, "Do Flowers and NCR bear play together?"

When first speaking to Ranger Milo he will inform the Courier that some "Legion snakes" are held up in Nelson, to which they can respond "Snakes are small. Why don't you just use a gun or whatever to shoot them." He will then call them a "special folk," and explain that they are not really snakes but "like snakes."

While helping Argyll in Nellis medical station while doing the quest Volare!, the Courier is given an option to "CHOP CHOP CHOP!" instead of giving him treatment. Ironically, the Courier actually saves the patient and Argyll comments on it, saying it was "dumb luck."