# Let's suppose vs. Let us suppose

Imagine you are working on a formal research paper (several authors). At the time of making an asumption, what would be more correct:

• Let us suppose that...
• Let's suppose/assume that...

The latter sounds better and more natural to me, but I want to make sure.

• A great deal depends on (a) the field involved and common usages there (in mathematics, for instance, there are traditions that prescribe), and (b) the supposition or assumption that is being hypothesized. Either contracted or uncontracted is OK, but probly one should settle on a single style for all uses, if it's used more than once. If it's for publication in a refereed journal, there may be a house style that the editor will enforce, so by all means leave it to the editor. Commented Apr 30, 2014 at 19:42
• Thanks John, in regards to Maths, what would you go with? Commented Apr 30, 2014 at 19:50
• Depends on what you're introducing. Normally in maths one uses the imperative, e.g. "Assume that the theorem is true for some value k, Assume a real vector space with the usual topology," etc. Or the old joke (guaranteed to get a laugh from a group of mathematicians) "Let G be a ring, let R be a field, and let F be a group." Commented Apr 30, 2014 at 20:10
• Actually depending on the context both could be too informal because of the us. Who is "us"? And why would I let you? Simply "suppose" is what you might have to use instead. Commented Apr 30, 2014 at 21:41

Contractions are best avoided in formal contexts. I would go with "Let us..."

• Thank you, honestly I didn't know "Let's" was a contraction of "Let us". Commented Apr 30, 2014 at 19:49
• In English, the vast majority of words with apostrophes in them are either a.) contractions or b.) genitives / possessives (in the singular possessive/genitive form, the apostrophe is there to distinguish the `s` that forms the genitive from the one used to form the plural of a noun, while in the plural it is present to mark the suppression of a second s). Commented Apr 30, 2014 at 19:57

To quote my former math professor: "Rule of thumb: Never do contractions in research papers, however unnatural they might sound to you."

Words to live by.

• Fist? Rule of fist? Huh?
– tchrist
Commented Apr 30, 2014 at 23:01
• Eh, rule of thumb. Commented May 1, 2014 at 0:22
• I like rule of fist! It sounds a lot more persuasive. Commented May 27, 2017 at 7:09