We can wonder about what others are thinking or feeling without ever hearing them say a word. 

My toddler holds an empty ice cream cone, looking despondently at a melting ball of goo on the ground. It is obvious that she is sad she lost her treat. An orangutan brushes his head with a leaf, then hands the leaf to a human caregiver. For anyone familiar with the orangutan sanctuary in Indonesian Borneo, it is clear the orangutan wants his head cleaned. An extraterrestrial spaceship is observed approaching Earth. Humanity hopes their intentions are peaceful.  

The ideas we have about young children's, animals' or aliens’ feelings and intentions suggest that it is possible to be a thinker without being a speaker. But some philosophers have denied it, arguing that only language users can believe anything. Understanding this view requires a little unpacking about what language and belief are.    

My daughter doesn’t yet use language. The orangutan, like all nonhuman animals, doesn’t have a natural language system. The aliens might not have anything like a human language; suppose they share a joint mind and communicate with one another the way subsystems of our body do. These beings can communicate, but they don’t use language—that human method of communication that has grammatical structure allowing us to create sentences, logical structure allowing us to make inferences from sets of sentences to new sentences, and which permits these sentences to have truth value.