Principle of compositionality

The Principle of Compositionality is like a rule for how words and phrases can be put together to create meaning. Let's say you want to make a sentence that means "The dog is eating an apple". You can make this sentence using the principle of compositionality. You start by taking two smaller pieces of the sentence, like "dog" and "eating". Then you put them together to make one piece that means "the dog is eating". You do the same thing with "an apple" to create the full sentence. It's like building with Lego blocks!