Functional theories of grammar are ways of understanding how words and phrases are used to convey meaning in a language. Think of it like building blocks - words and phrases can be put together to make sentences, just like you can use blocks to make a tower or a house.
Functional theories look at how language is used in real-life situations, like talking to friends or giving directions, and how different parts of a sentence work together to convey meaning. This is different from other theories that focus more on the structure of language itself.
A big part of functional theories is understanding the different functions that words and phrases can have in a sentence. For example, a subject is usually the person or thing doing the action in a sentence, like "I ate the apple." The verb is the action being done, like "ate." And the direct object is the thing that the action is being done to, like "the apple."
By understanding how these different parts of a sentence work together, we can better understand how people use language to communicate. For example, you might describe a character in a book by saying "she had long, curly hair and big green eyes." Here, the different descriptive phrases are all working together to help you create a mental image of the character in your mind.
Functional theories also look at how languages change over time and how different cultures use language differently. For example, some cultures might use more formal language when addressing someone who is older or in a position of authority, while others might use more informal language with their friends and family.
Overall, functional theories of grammar help us understand how people use language to communicate and express meaning, and how different parts of a sentence work together to create that meaning.