"They know when their knowledge ends and say something to the extent of 'i don't know and anything else i say on this topic is ignorant speculation.'"

8. They know what they don't know.

"They aren’t afraid to say they don’t know the answer to a question."

10. They don't pretend to know everything.

"They effortlessly communicate complex concepts in a simple way.

7. They make hard ideas simple.

"They are curious about everything. To be intelligent you need to be knowledgeable and you can't be knowledgeable if you are never curious,.

4. Curiosity.

"When they explain something they make you feel intelligent."

5. They're great at conveying ideas.

"They can ask really good questions." <ol><li>"Edit: to anyone not understanding what mean, I’m talking about people who ask “really good questions”, not just any questions, really good ones. I don’t know how one would achieve this skill(I know I haven’t).</li></ol>

9. They ask great questions.

"They admit to changing their mind about something.

11. They change their minds with new information.

"Admitting when they're wrong and being willing to learn from mistakes."

16. They learn from mistakes.

"They can genuinely consider an idea which opposes their worldview without necessarily accepting it

13. They are open-minded.

One of the strangest things about being human is that people of lesser intelligence tend to overestimate how smart they are and people who are highly intelligent tend to underestimate how smart they are. This is called the <a href="https://www.deanyeong.com/article/dunning-kruger-effect">Dunning-Kruger effect </a>and it’s proven every time you log onto Facebook and see someone from high school who thinks they know more about vaccines than a doctor. The interesting thing is that even though people are poor judges of their own smarts, we’ve evolved to be pretty good at judging the intelligence of others.

18 Signs That Someone Is Really Smart

"They say they love learning and they learn something new every day. Then they listen more than talk.

18. A love of learning.

"They draw wisdom from multiple sources. Wait but that might be more wise than intelligent... But I guess those two tend to be seen together a lot.

1. They draw wisdom from multiple sources.

"I used to work with a doctor - Tom Howard - and the day I realized he was a genius was the time he guessed every single condition a patient of mine had based on minute pieces of information about him.

3. They develop a keen sense for their job.

"They can switch up the way they talk to match the person they're talking to without sounding condescending. They listen to how others learn and explain it in that person's language of understanding.

2. They know their audience.

"People who use analogies to explain concepts to others. It’s a form of code-switching and integrating concepts on the fly and is a clear indicator someone is both socially and conceptually intelligent.

14. They use analogies.

"Humor. I think that truly funny people are often very smart and cognizant of the different ways an idea can be humorous on several levels. They also know their audience. I think the difference between say a Jeff Foxworthy and a Dave Chappelle and a Bo Burnham is their audience and their interests.

17. A sense of humor.

What is a subtle sign that someone is really intelligent? They tend to be great communicators who understand their audience and are more concerned with getting things right than being right.

Concern With Getting Things Right 

"They spend time thinking before asking a question.

6. Considerate questions.

"They apply knowledge from one realm into a new and relevant situation.

12. They pivot well.

"I think intelligent people are more willing to calmly debate/discuss, rather than argue. Like, you explain to them why you disagree, and they listen to you and ask further questions about your viewpoint before offering a different perspective; as opposed to an unintelligent person, who would just resort to insults when other people disagree with them"

4. Curiosity.

Similar ideas to 4. Curiosity.

Curiosity

Predicting curiosity

George Loewenstein's theory on curiosity