The phrase "cannot vary" is correct and usable in written English.
You could use this phrase when talking about something that is unchanging or unchangeable. For example: "The temperature of liquid nitrogen cannot vary."
This case provides us with a specific ethical supervenience thesis: it suggests that the ethical quality of the manager's action cannot vary without something else varying as well (compare Horgan and Timmons 1992, 226 on specific supervenience facts).
Cases like this one seem to show a necessary connection: they suggest that the ethical character of the bank manager's act cannot vary without some other facts varying as well.
On these measures, the walls cannot vary more than a quarter of an inch.
Terms of coverage cannot vary based on the age of young adults under 26.
The numerical solution of singular perturbation problems (SPPs) is delicate because the perturbation parameter ε and the mesh size h cannot vary independently of one another.
Responsive traffic plans only partially solve this problem, since they cannot vary continuously the traffic light settings, and generally consider only the input flow variations.
give, and cannot afterwards vary it if they do not conform to the contract.
The Welsh government cannot currently vary taxes or borrow money, and instead gets its budget in a grant from the UK government.
It must not be overlooked, however, that some of the conditions cannot be varied, and their effects cannot therefore be examined in this way.
In fact, the crack position cannot be monitored during ECT tests and the crack length cannot be varied by repositioning a single specimen.
