In Deuteronomy the priests are called הַכֹּהֲנִים הַלְוִיִּם. In Leviticus they are בְּנֵי אַהֲרֹן הַכֹּהֲנִים or הַכֹּהֲנִים בְּנֵי אַהֲרֹן. Ever wonder why?
The theory of the critics is that Leviticus is the work of Aaronid priests who were protecting their prerogatives. They wanted it perfectly clear that they, and not anyone else, were the true priests. Outside of the material attributed to the Aaronid priests (specifically Deuteronomy) the priests are often called הַכֹּהֲנִים הַלְוִיִּם, which say the critics, suggests some sort of rivalry between the Levites, or a family of Levites, who thought they were entitled to serve in the Temple or bring offerings and the Aronids who wanted it made clear that right belonged to them, and them alone. (Preceding shared for informational purposes only. DovBear is not trying to steal your soul and he may not even accept the truth of the summary he has just shared.)
Being honest: I don't know how the Rabbinic interpreters dealt with this inconsistency. Can someone point me to their solution?