Personality

In both The Sims and The Sims 2, personality is split into 5 sections: Niceness, neatness or cleanliness, outgoingness, activeness, and playfulness. It is normally related to a Sim's Zodiac sign, but there are exceptions. If a Sim's personality is altered without using cheats, his or her Zodiac sign will not change. Also, spore-grown PlantSims will inherit their spore-parent's personality, but will have a different Zodiac sign.

Each section uses a zero-to-ten scale. (From a game-mechanics perspective, the scale is actually 0 to 10.00. How fractional points are handled appears to depend on the game, and possibly the scale.) In The Sims, each section is split into three parts; 0-2, 3-7, and 8-10, each of which has a name and a description. The descriptions are largely for "color", but do give some hints to the Sim's character. Still, in The Sims, this has relatively little effect on the nature of the Sim. Personality has much more effect on a Sim's nature in The Sims 2. The Sims 2 does not use the labels or descriptions, but personality scales can be divided into low, medium, and high. In The Sims 2, low is generally less than 4 or 5, and high is generally 8 (or 8.01) and above. In The Sims 3, the personality points system was replaced with traits.

In The Sims, children get personality points when they grow up from being babies. There were varying reports as to how (and whether) the parents' personalities affected the child's. Most townies get random personality points, though they may not receive them until they first appear in-game. In The Sims 2, the personality of children born in-game is based on the parents' personalities, though there is a random element involved; twins may have different personalities. It is also affected by how the child was raised as a baby. A neglected baby might be more mean-spirited, even if both parents are nice, for example. A baby's personality is not visible in-game, but can be viewed with SimPE. Adopted children and townies always seem to get one of the 12 default personalities in Create a Sim.

Altering personality
Personality can be altered in variety of ways.

The Sims
In The Sims: Livin' Large, the chemistry set can make a potion that reverses personality points. The only way to get them back would be to recreate the potion. A Sim abducted by aliens would return with an altered personality. Sims can change their personality one point at a time by using the Crystal Ball. Also, a zombie would have no personality at all.

The Sims 2
In The Sims 2, a Sim's older relatives can influence that Sim to gradually change some aspects of his or her personality by using the "Encourage..." interaction. The two Sims do not have to be members of the same household, and the Sim being Encouraged does not have to be selectable. For example, a Sim can Encourage his or her visiting grandchildren. The ability to Encourage is not unlimited; which scales the older relative can influence, and which direction he/she can influence them in, depend on his/her personality. Changing personality this way is very slow; adding or subtracting one personality point requires several "Encourage..." interactions. The effectiveness of an "Encourage..." interaction depends on three factors. One is the younger Sim's relationship with the older. If it is too low, the interaction will fail; otherwise, a higher score will generally produce a larger change. A second factor is the difference between the two Sims' scores on the personality scale in question. The third factor is the age difference between the two Sims. In both cases, the greater the difference, the stronger the effect. Toddlers cannot be Encouraged. Young adults are counted as adults for purposes of the "Encourage..." interaction, so adult parents cannot Encourage their college-student offspring. Sims may occasionally get a want to Encourage their offspring. These wants appear more often to Sims with the Family aspiration.

With the boolprop testingCheatsEnabled cheat, the player is able to drag a Sim's personality points at will. This will also change the Sim's zodiac sign.

If Apartment Life is installed, a Sim can drink the "Magically Spiced Sugar" potion and temporarily get 10 niceness points or drink the "Enchanted Essence of Cur Tails" potion and temporarily get 0 niceness points. Both potions can be crafted by witches/warlocks or bought at the secret magic lots.

Qualities
These qualities are sometimes referred to as "traits", but should not be confused with traits as implemented in The Sims 3 and The Sims Medieval.


 * Shy/Outgoing
 * Outgoing Sims love to perform social interactions and often exhibit happy reactions when the player commands them to socialize. They will often use a mirror autonomously. The social bar of outgoing Sims decays rapidly, as they desire social interaction. Sims who are extremely Outgoing (8 points or higher) will enter hot tubs naked, assuming there are no teens or children around. Outgoing Sims also do not mind using the toilet in front of other Sims, regardless of relationship. In The Sims 2, Sims who are extremely Outgoing will not automatically change into their everyday clothes when leaving a lot. In The Sims, Outgoing Sims enjoy watching the romance channel on TV. It's been realized that the Outgoing Sims randomly come into Sims' houses for a visit, even if they don't know any Sims on that lot.
 * Shy Sims dislike social activities, and if told to do so, will often grimace at the camera, and walk to the activity slowly with head bowed. Also, while walking from place to place, Shy Sims sometimes wring their hands and look anxious; this is one way to identify shyness in townies and NPCs. They are fearful about diving into pools and will often back away off the diving board after getting on it. When being admired, a shy Sim will act very timid. The main benefit of shyness is that a Sim's social bar decays more slowly. In The Sims 2, shy Sims can fear using a photo booth or karaoke machine, even though they'll sometimes want to sing a duet with another Sim. Shy Sims would rather chat online on the computer than talking in person to people.


 * Grouchy/Nice
 * Nice Sims are usually kinder to other Sims, and will probably respond positively to a social interaction, even if they aren't interested in it. For example, Nice Sims are likely to accept the "Admire" interaction from other Sims even if they don't know each other well. Also, Nice Sims will listen politely to Grilled Cheese Sims talk about grilled cheese even if they aren't interested in it themselves (most Sims really don't want to hear about grilled cheese unless they share that aspiration). If a nice Sim is attacked in a way, like poking or shoving, they will not attack back. If a Sim with 5 nice points or more is insulted, they will usually cry, rather than insult back.
 * Grouchy Sims are more likely to react negatively to social interactions. They are also more likely to initiate negative interactions with other Sims (teasing, pranking Sims they don't know, etc.) In The Sims 2, they may come onto a residential lot to steal the newspaper or kick over the garbage can, even if they have no relationship with any Sims who live there—or even if one of their friends lives there. Also in The Sims 2, they are more likely to cheat in games, and may cheat autonomously. When playing catch or having a snowball fight, they may throw hard. When playing the game Punch U Punch Me, they may punch unforgivably hard. Sims with 2 nice points or less will practice lecturing when using the Politics or Law career rewards. In The Sims, Grouchy Sims enjoy watching the horror channel on TV.


 * Serious/Playful
 * Playful Sims can jump on sofas, play in bathtubs, and even play with refrigerator doors. Sims with at least 5 Playful can also skip from place to place; players can have them do this by clicking on the ground and selecting "Skip Here," which is faster than walking, though not as fast as running. In The Sims, Playful Sims enjoy watching the cartoon channel on TV. In The Sims 2, Sims who are extremely Playful (8.01 or above) cannot meditate. Sims with 8 playful points or more will practice telling jokes when using the Politics or Law career rewards. Some Playful Sims also have bad sides, as they may autonomously tease fellow acquaintances, regardless if the teasing Sim is Nice.
 * Serious Sims dislike watching TV and prefer reading. Should such a Sim be told to read they will smile at the camera and punch the air. They will also react this way when being directed to play chess or look through a telescope. However, though serious Sims autonomously choose reading and the like over TV, the actual gain to fun from watching the TV is no different than if a Playful Sim watched it. In The Sims, Serious Sims will enjoy watching the news channel on TV.


 * Sloppy/Neat
 * Neat Sims like cleaning activities, even gaining Fun from doing them. They are more likely to clean or make beds autonomously, and may autonomously 'groom self' in the mirror. They exercise good table manners (the drawback to that is that it takes them longer to eat) and are likely to wash their dishes when finished, sometimes even cleaning up other dishes at the same time. They are more likely to flush toilets autonomously, and in The Sims, are more likely to autonomously wash their hands after using the toilet. Because of their clean attitude, their hygiene decays slower. Neat Sims clean more quickly. Sims who are extremely Neat (9 or 10 Neat) have a special feature: they create sparkly bubbles when they clean household objects. This gets the objects "ultra-clean" instead of just clean, but takes (very slightly) longer. Neat Sims can have a fear of using a public toilet. In The Sims 2, extremely Neat Sims who are pregnant may be able to throw up without causing the toilet to need cleaning. In The Sims 2: FreeTime, extremely Neat toddlers who play with blocks at the activity table may put the blocks away.
 * Sloppy Sims prefer to make messes and can also rummage through the trash can for food. They dislike cleaning, and actually lose a small bit of fun when forced to do it. Due to their messy nature, their hygiene decays faster, though they seem to care less about it, and objects such as showers and counters get dirty more quickly when Sloppy Sims use them. If they are very Sloppy, they tend to generate large puddles around the showers and bathtubs they use, and often relieve their bladder when using said showers. Sloppy Sims eat messily (but quickly), and they tend to flatulate more often than other Sims; both of these activities will disgust any Neat Sims who happen to notice them. Another drawback is that Sloppy Sims may autonomously eat rotten food, which can of course make them sick. However, one benefit is that a Sloppy Sim will autonomously take a sponge bath in the nearest sink if his/her hygiene drops low enough; this can come in handy if no shower or tub is available (Sloppy Sims can only do this via free will, not on command). A Sloppy Sim will find having low hygiene amusing, but they will still autonomously use a bath or shower to improve their hygiene. Sloppy Sims can have a fear of cleaning up a mess.


 * In The Sims 2, this score affects whether or not the Clean interaction appears when clicking on an object that can be cleaned. The neater a Sim is, the less dirty an object has to be before the Clean interaction will appear.


 * Lazy/Active
 * Active Sims lose energy slower than anyone, and they enjoy working out. Sims with at least 6 Active can be directed to run to get somewhere (lazier Sims will only run if the location they're going to is far away). However, due to all this activity, their hunger decays faster too. Active Sims also gain Body skill faster than normal, due to their active nature, and their fitness level goes up more quickly when they exercise. In The Sims, Active Sims enjoy watching the action channel on TV.
 * Lazy Sims can be identified by the slouched posture they take on when standing still. Their energy motive is quick to decay, and it also takes longer to replenish, meaning that when they go to sleep they tend to stay in bed longer than Active Sims do. Also, due to their 'couch potato' nature, their comfort decays faster too, making them need to sit or relax more often. And, as a side effect to all of this laziness, their hunger decays more slowly. The Logic skill comes most naturally to Lazy Sims, since building that skill involves mostly sedentary activities. In The Sims, Lazy Sims who wake up before their Energy bar is completely filled will do a "mad dance" after getting out of bed, though they will not do this after napping on a sofa or in a recliner. Lazy Sims can go to sleep while their energy motive is still high (but not completely high).


 * In The Sims 2, this score affects how low a Sim's Energy bar needs to be before the Sim can sleep in a bed. The less active a Sim is, the less their energy needs to drop before the Sleep interactions will appear when clicking on a bed.

Personality and skill-building in The Sims 2
A Sim's personality has a fairly pronounced effect on how quickly they can build skills from certain activities. Usually, this takes the form of a bonus to Sims with the favored personality (which is larger the more extreme their personality is), with Sims who have exactly 5 points in the personality trait or who have the non-favored personality getting no bonus. For example, Sims with 0-4 Playful gain logic faster than Sims with 5-10 Playful, and a Sim with 5 Playful will gain logic at the same speed as a Sim with 10 Playful.


 * Body
 * Active Sims gain Body more quickly when exercising.


 * Charisma
 * Outgoing Sims gain Charisma more quickly when practicing speech or romance at a mirror, or when using the Execuputter career reward.
 * Playful Sims gain Charisma more quickly when teaching a pet bird to talk or talking to it.


 * Cleaning
 * Neat Sims gain Cleaning more quickly when studying cleaning from a book or when cleaning household objects. The effect is more pronounced when cleaning things; additionally, when actually cleaning something, the speed at which they learn the skill scales across the entire range: a Sim with 0 Neat will learn more slowly than a Sim with 1 Neat. For Sims with 0 Neat, cleaning will actually build the skill more slowly than studying cleaning—for Sims with 2 Neat or more, the opposite is true.


 * Creativity
 * Playful Sims gain Creativity more quickly from playing musical instruments. This is true for both practicing and performing, but the effect is larger for performing. For Sims with 9 or 10 Playful, performing builds the skill faster; for Sims with 7 or less Playful, practicing is faster.
 * Playful Sims also gain Creativity more quickly from writing a novel on a computer, using the SensoTwitch Lie Finder career reward, and tending the AquaGreen Hydroponic Garden career reward.
 * Shy Sims gain Creativity more quickly from painting on the easel.


 * Logic
 * Serious Sims gain Logic more quickly from playing chess (either with another Sim or solo), and from using telescopes.

Personality Descriptions from The Sims

 * Neat
 * Slob (0-2): So I occasionally leave a pizza box or two laying around, and I don't mind the flies buzzing all over. Why clean up when everyone else is willing to do it?
 * Occasional Cleaner (3-7): When it comes to cleaning up I have a few basic rules. I flush when I'm done, clean up my own junk and take out the trash now and then.
 * Neat-Freak (8-10): I'm known to wash dishes as soon as I'm finished eating. The trashcan's barely full before it's taken out. The paper is recycled as soon as I'm finished reading. And the house is always spotless whenever I'm about.


 * Outgoing
 * Shy (0-2): Being self-conscious and introspective, I don't have a great need to be social. It's hard for me to meet new people and make friends.
 * Member of the Crowd (3-7): I'm a little reserved, and it takes me a while to warm up to new people. You won't see me in the middle of huge crowds at parties, but I won't be sitting quietly in a corner either.
 * People Person (8-10): I'm an extrovert. I love to talk to everyone. I crave social interactions. Basically, I'm a social animal.


 * Active
 * Lazy (0-2): Is there anything worse than getting out of bed in the morning? Who needs ambition--a warm couch and a good TV show is all anyone needs.
 * Laid Back (3-7): Though not always on the go, I am somewhat motivated. Though I tend to linger a little too long in a nice cozy chair, I won't be caught sitting there all day either.
 * Energetic (8-10): Some say I'm a live wire. Some say I have ants in my pants. Either way, it just means I'm always on the go and anxious to get there.


 * Playful
 * Serious (0-2): Sims who spend their time joking just irritate me. Don't they understand that their frivolous folly is meaningless? So much more fun can be gained by reading a good book.
 * Amused (3-7): I laugh at good jokes, dance if there are other people on the floor, and like to play games. Generally, I like having fun but I don't go overboard.
 * Life of the Party (8-10): When I'm not telling jokes, I'm laughing at them. I've never seen a game I didn't want to play. That's why everyone knows the party is always at my house.


 * Nice
 * Mean (0-2): Everything makes me mad, especially when someone says I have a temper. If everything wasn't always broken, or other Sims weren't always bothering me, I probably wouldn't have to blow my stack so often.
 * Easy Going (3-7): While some Sims can get on my nerves a little, overall I'm pretty good-natured.
 * Compassionate (8-10): I like giving hugs and compliments. I love making friends with everyone. If everyone were more like me, the neighborhood would be a nicer place.