# Using "that" for nested subordinate clauses

I wrote

Suppose that you know that 10% of people are smokers.

Are using of two "that" natural? Can I say it in other ways and omit one or two "that"s?

It's perfectly good, and reasonably natural.

You could omit either or both of the thats.

Omitting the first one is quite natural.

Normally, omitting the second would also be natural; but in this case it might be confusing, because of the alternative meaning of "know", as "be acquainted with", so the resulting sentence could be a "garden path" sentence (You might think it was saying "Suppose you know 20% of people ... " and have to reparse when you hit "are").

• +1 for pointing out the risk of garden path parsing when you omit the second that. Commented Mar 14, 2016 at 11:02

Suppose that you know that 10% of people are smokers. [emphasis mine]

What is atypical, if not unnatural, here, given the usual way such statements are used, is not the use of that but that the content of the supposition is knowledge of a fact rather than the fact itself.

Also, with percentages, it's typical to say population not of people.

Suppose one in ten people is a smoker.

or

Let's suppose 10% of the population smoke(s).

• Yes, I took it that this was a step in an argument about knowledge and evidence, not an argument about material facts. Commented Mar 14, 2016 at 16:07