The phrase "a critical assumption" is correct and usable in written English.
You can use it when discussing an important belief or premise that underlies an argument, theory, or analysis.
Example: "In our research, we identified a critical assumption that must be validated for our conclusions to hold true."
Alternatives: "a key assumption" or "an essential assumption".
And a critical assumption for Professors Mankiw and Weinzierl is that government spending falls to keep the budget in balance.
A critical assumption in implementing all forms of PSDA is the selection of the seismic Intensity Measure(s) used to correlate structural response to ground motion characteristics.
A critical assumption underlying the use of functional localiser scans is that the voxels identified as the functional region-of-interest (fROI) are essentially the same as those activated by the main experimental manipulation.
Although the diffusion of innovation theory suggests five adopter categories according to their degree of innovativeness, this approach lacks theoretical justification and, more importantly, it makes a critical assumption of a normal distribution of adopters that needs empirical validation.
A much more serious limitation of ASP linkage analysis is the implicit assumption that randomly sampled sib pairs share half their alleles identical by descent at any locus, whereas a critical assumption underlying Vieland and Huang's proof is that of joint Hardy-Weinberg equilibrium proportions at two trait loci.
A critical assumption is that the true detectability increases with increased defect size.
For example, there has been a longstanding critical assumption, based on generalized notions of the eucharist, that the development of a strong Anglican aesthetic brought about a distrust of figurative language and in turn a distrust of figurative or allegorical interpretation.
A third critical assumption is that glucose taken up by liver, and phosphorylated, is not immediately converted to liver glycogen.
A second critical assumption of SOP is that when two items are associated, presentation of one will place elements of the other directly into the secondary activation state.
I take Lewalski's critical suppositions as a representation of a much wider critical assumption which seems to operate unreflexively.
And they are based on at least a couple critical assumptions.
