According to Seth MacFarlane, himself, everyone IS able to understand Stewie full well. However, characters such as Peter and Lois just choose to ignore him the way most people do with children, believing in the idealism that “Children should be seen and not heard.”
Major characters who can and can't understand Stewie Griffin.
- Stewie Griffin - (obviously)
- Brian Griffin - Brian is one of the most prominent characters to have full-fledged conversations with Stewie. Their relationships with each other are the strongest relationships both of them have ever had with anyone.
- Chris Griffin - Chris has proven on a few occasions that he can understand Stewie completely.
- Meg Griffin - Meg has had a number of conversations with Stewie, proving she understands him.
- Herbert the Pervert
- Mayor Adam West
- Dr. Hartman
- Neil Goldman
- Seamus Levine
- Loretta Brown
- Susie Swanson
- Rallo Tubbs
- Jillian Russel-Wilcox
- Ida Davis
- Vinny Filipeli
- Jess Griffin
- Lois Griffin - Stewie has spoken directly toward Lois many times in the show but most of Lois' dialogue in response has usually been vague enough to make it seem like she doesn't hear him.
- Peter Griffin - Peter doesn't understand anything Stewie says.
- Carter Pewterschmidt
- Babs Pewterschmidt
- Carol West
- Glenn Quagmire
- Cleveland Brown
- Joe Swanson
- Miss Tammy
- Tom Tucker
- Diane Simmons
- Joyce Kinney
- Mort Goldman
- Mr. Weed
- Bonnie Swanson
- Donna Tubbs-Brown
- Kimi Quagmire
- At the end of “E. Peterbus Unum”, a college course in the year 3000 was studying a Family Guy episode from thousands of years ago. One of the students asked the instructor if people were able to understand Stewie or not.
- In “Untitled Griffin Family History”, Peter said that he found the movie The Godfather to be so boring that he couldn’t even get through the whole film. Stewie asked Peter, “How do you know you don’t like it if you didn’t watch the whole thing?” Lois added, “I agree with Stewie. How do you know you don’t like it if you didn’t watch the whole thing?” This exchange of dialogue proves that Lois understands exactly what Stewie says at all times.
- In “Love, Blactually”, Stewie and Brian went to visit Loretta. Stewie said that he would be doing all the talking but Brian assured him that Loretta wouldn’t understand him. Stewie assumed that Loretta was one of the minor characters who can understand him perfectly fine but Brian said that because of her connection to the major character of Cleveland, she’s the kind of person who would only get the gist of what he’s saying. This banter went on for a while until a guy from the camera crew said “We’re filming!” When talking to Loretta, the latter said she got the gist of what he was saying.
- In “Lois Kills Stewie”, Stewie held Brian at gunpoint and told him to talk to Joe. Stewie fed insults to Brian and Brian said them all. Joe understood him and his whole day was ruined.
- In “Herpe the Love Sore”, Peter had a whip and Stewie told him that he had a cool whip. Annoyed with how Steaie phrased that, Peter whipped him out cold.
- In “Dead Dog Walking”, Stewie told Chris’ secret to Peter, pissing Chris off. Stewie said that he didn’t think Peter would understand him and Peter said that he understood pieces every now and then.
- In “Pawtucket Pete”, Brian repeated an insult that Stewie said, getting him smacked in the face by Peter. Brian tried to explain that he was just copying Stewie but Peter wasn’t buying it. Stewie leaned back and said “Ah, the benefits of nobody understanding me.”