I am writing a scientific paper.
I am not sure about the usage of "assume."
Should I say "Let us assume x is real," or should I say "Let us assume x be real"?
English Language Learners Stack Exchange is a question and answer site for speakers of other languages learning English. It only takes a minute to sign up.Sign up to join this community
Your question has made me think about this for the first time: there seems to be a distinction between verbs that merely process information about a fixed situation, and verbs that declare a position or approach to a potentially changeable situation.
For example you would say
I believe [that] X is real.
and not "I believe X be real". By contrast you should really say
I demand [that] X be real.
and not "I demand X is real".
One result of this is that the following two statements have different meaning:
I insist that X is real
means "I emphatically believe that the proposition 'X is real' describes the current situation correctly, independent of my intervention or yours", whereas
I insist that X be real
means something along the lines of "I am laying down the law, that you must ensure X is real", or more generally "X may be real or not, but if it is not real then I will refuse to proceed/cooperate with whatever we're talking about".
Your example, of assuming whether something is real, is processing information about a fixed proposition. Therefore you would not use the subjunctive. You would say "assume that X is real", not "assume that X be real".
In a mathematical paper where are you are describing your initial conditions, you can choose whether to use the metaphor of actively creating X as you define it ("let X be a real number") or the metaphor of merely describing the state of an already-defined entity ("assume X is a real number"). The former is probably more common.