"should not suppose" is grammatically correct and can be used in written English.
It is typically used in formal or academic writing to express a warning or advice against making assumptions. Example: "In order to accurately assess the situation, one should not suppose that all individuals will react the same way to a given stimulus."
We should not suppose that all creatures deploying this strategy can engage in the kinds of self-conscious deliberate imagining that we do.
But the Americans should not suppose France shares their own or specifically George Bush's view of the world in general and Iraq in particular.
But his former colleagues in the Administration should not suppose that his potential invocation of the Fifth magically extends to their offices, in terms of a refusal to, for example, produce documents that Congress or investigators might require.
Standing on the edge of a cliff, she should not suppose that if she were to jump, she would have a parachute to break her fall.
We should not suppose that we can derive much philosophical value from Plato's writings if we refuse to entertain any thoughts about what use he intends us to make of the things his speakers say.
Levy (2004) has argued that non-intentional accounts of self-deception that deny the contradictory belief requirement should not suppose that self-deceivers are typically responsible, since it is rarely the case that self-deceivers possess the requisite awareness of the biasing mechanisms operating to produce their self-deceptive belief.
They are right to conclude that public engagement is important, but they shouldn't suppose that explaining the science will banish all these misgivings.
In 2001, the prime minister said people "shouldn't suppose" that a second Labour victory would produce increases in national insurance.
The acquisition of cellular technologies fingerprint data should also not suppose any significant cost in terms of the calibration phase, as the cellular scenario characterization can be performed simultaneously to the RFID one.
Mr. Kern has injured his health in past campaigns by his activity, and as he means vastly more to me than any political honors, I am sincerely sorry, although I suppose I should not say so".
Richard's role in ending the Revolt was rightly acclaimed, but it should not be supposed that he was influential in making policy.
