Associating users with nested models in rails

Question

I just added users to my app using Authlogic and CanCan. I just have a quick question about best practices for associating users to my other models.

I have 3 models that are nested within each other with one-to-many associations like this:

SENTENCE > WORD > LETTER

So a sentence has many words, and a word has many letters. I am just wondering if I need to associate users with just the SENTENCE or with WORDS and LETTERS too.

So should a user just have many sentences, or should they also have many words and many letters too. The way my app is set up, you can't create words without sentences and you can't create letters without words - so I was confused if I really needed to associate the nested models with the user or not - thanks!