I have read here that there is no consensus about the usage of a priori as italic or not. However, increasingly it is used as non-italic.
And here I read the following text:
"In fact the a priori reasoning is so entirely satisfactory to me that if the facts won’t fit in, why so much the worse for the facts is my feeling. [Erasmus Alvey Darwin in a letter to his brother, Charles Darwin (1859)]"
In my own text in a submitted paper, I have the following sentence:
"Additionally, the a priori probabilities in our work are not required to be equal"
The editor called "the a" as a typo. This is not important at all because the work is fairly a technical work and such grammatical issues are not the most important in such works.
However, I really wonder, whether the usage "the a priori..." is correct and if not how one could resolve the issue.