The phrase 'we cannot assert' is correct, and it can be used in written English.
You can use this phrase when you want to express doubt or uncertainty about something. For example, you might say, "We cannot assert whether the dropped pencil was yours or your brother's".
Colin McKay, head of Salmond's strategy unit, told a seminar of constitutional lawyers: "We cannot assert as an a priori fact we can achieve a currency union with the UK, but we can set out why we think it is the best option".
That is, we cannot assert that we can achieve a certain population from nonnegative controls.
In general, we cannot assert that the set Λ is closed in (L^{p}(Omega)).
Clearly, we cannot assert if spambot data does or does not represent botnet owners and controllers.
We cannot assert the same comparing nearly equiangular frames to incoherent UNTFs obtained with [26] and [30].
Although we cannot assert that all explanations are based on causal interaction, seldom will doubt the central position of causal relationship in scientific explanation.
However, we did not measure CBF directly in the present study and so cannot assert that this is the origin of the positive response.
"We believe the documents withheld by Lay are corporate records of Enron and that Lay cannot assert a personal Fifth Amendment right as a basis for withholding such documents," Luis R. Mejia, a lawyer for the S.E.C., wrote to Mr. Lay's lawyers in a letter dated last Wednesday.
In other words, one person cannot assert a claim on behalf of another.
Texas cannot assert any legitimate state interest here, such as national security or preserving the traditional institution of marriage.
The general counsel, Robert E. Fabricant, issued a memorandum that said "E.P.A. cannot assert jurisdiction to regulate in this area".
