Why is "I find this article is interesting" grammatically incorrect?

Question

1. I believe that you are a good person.
2. I believe you are a good person.
3. I find that this article is very interesting.
4. I find this article is interesting.
5. I find this article interesting.

I know that sentence number 4 is incorrect but can you give a grammatical explanation why? Why can't we lose the "that" like in sentences 1 and 2. If any of the rest of the sentences is incorrect please point it out. Thanks.

Answer 1

Sentence 4 is perfectly good, but less common than 5.

As you surmise, 4 is similar to 3, and equivalent to I find that this article is interesting, which has a different meaning from 5.

4 means "I discover that this article is interesting" whereas 5 means "I judge or experience this article as interesting". They might be said in the same circumstances, but they are expressing different mental processes.