1. Do you have anything to say about this?

2. Do you have to say anything about this?

(Are both grammatical and the same?)

3. We have many things to do.
4. We have many things that we have to do.
5. We have many things that we will do.

(If we pharphrase #3, can we get #4 or #5? Which one is more similar to #3, #4 or #5? Or do we have another better equivalent?)

1 and 2 are grammatical, yes, but they don't quite mean the same thing.

#1 is asking if you have anything to add to or answer about whatever "this" is.

#2 is asking if a person must add information to whatever the topic is.

#3 is the best phrasing. #s 4 and 5 are wordy repeats of #3.

1. Yes, both sentences are grammatically correct.

2. Yes, both sentences are grammatically correct.

Regarding the meanings of the two sentences, they are slightly different. "Do you have anything to say about this?" implies that you are open to hearing the person's thoughts or opinions on the matter, but you are not necessarily expecting a response. On the other hand, "Do you have to say anything about this?" could be interpreted as asking if the person feels obligated or required to say something about the matter.

3. If we paraphrase sentence 3, we can get sentence 4 or 5. Both sentence 4 and 5 convey a similar meaning to sentence 3, but there are slight differences in their structure and emphasis.

Sentence 4: "We have many things that we have to do." This sentence emphasizes the obligation or requirement to do these tasks. It suggests that there are tasks that need to be done and implies a sense of responsibility or duty.

Sentence 5: "We have many things that we will do." This sentence emphasizes the intention or plan to do these tasks. It suggests that there are tasks on the agenda or in the future plans.

If you want an equivalent to sentence 3 while maintaining its structure, sentence 4 would be more similar. However, if you are open to a different structure that conveys a similar meaning, both sentence 4 and 5 could be considered equivalent alternatives.