ELI5: Explain Like I'm 5

formal language theory

Formal language theory is like playing with different kinds of Lego blocks, but instead of making a tower or a castle, we use the blocks to make rules about languages. These rules help us understand how languages work and how to build new ones.

Let's say our language is made of only two letters, "a" and "b". We can use Lego blocks to make rules about this language. We can use a yellow block to say "if we see an 'a', then we must see a 'b' next". Or we can use a blue block to say "we can repeat any number of 'a's before we see a 'b'".

By putting these Lego blocks together, we can make even more complex rules. For example, we can use a green block to say "we can repeat the pattern of 'a's and 'b's any number of times, as long as it starts and ends with 'a'".

These rules can help us understand which words are allowed in the language and which are not. For example, "abab" and "aaabbb" are allowed, while "bbaa" is not allowed.

There are many different Lego blocks we can use to make rules for different kinds of languages. Formal language theory helps us study these rules and create new languages, just like building with Lego blocks helps us create new structures.