The phrase "a principal difference" is correct and usable in written English.
It can be used when discussing the main or most significant distinction between two or more items, concepts, or ideas.
Example: "One principal difference between the two theories is their approach to understanding human behavior."
Alternatives: "a key difference" or "a major difference".
A principal difference that may explain the different results between these studies is the different isotypes used to stimulate the BCR, such as IgM only; IgM and IgG; or IgM, IgG and IgA.
A principal difference between the effects of plasma on materials with the pores of different sizes is demonstrated.
A principal difference between oxide and hydride fuels is the high thermal conductivity of the latter.
"There is no need to be concerned with sales or other commercial matters," she added, underscoring a principal difference between corporate-sponsored galleries and those that are independent.
A principal difference between over-the-board chess and all forms of correspondence chess is that in the latter players are permitted to analyze a position by moving the pieces and by consulting reference books.
A principal difference between the current and former umbrella units, Interpublic executives said, is that under Mediabrands the media agencies would retain autonomy and remain aligned with advertising and marketing agencies like the McCann Worldgroup (Universal McCann) and Draft FCB (Initiative).
"You feel it in your chest when you're in front of that car on the race track," he added, "It's absolutely a different thing — and the principal difference is the engine".
The diagrams in Figure 12 illustrate in a simplified manner the principal difference between the two contraction mechanisms, that at a cleavage furrow and that at a phagocytic cup.
But the pre-primary debates over the weekend made it clear that the slogan is a reminder of the principal difference between Mr. Huntsman and the front-runner, Mitt Romney: Mr. Huntsman, the Obama administration's former envoy to Beijing, appears to believe what he says.
This is the principal difference between a dog and a man". I've also liked "Concerning the difference between man and the jackass.
This is the principal difference between a dog and a man.
