On parle en général de [licence **de** mathématiques](https://books.google.com/ngrams/graph?content=licence+en+math%C3%A9matiques%2Clicence+de+math%C3%A9matiques&year_start=1800&year_end=2000&corpus=7&smoothing=3&share=&direct_url=t1%3B%2Clicence%20en%20math%C3%A9matiques%3B%2Cc0%3B.t1%3B%2Clicence%20de%20math%C3%A9matiques%3B%2Cc0) ou [**de** lettres](https://books.google.com/ngrams/graph?content=licence+en+lettres%2Clicence+de+lettres&year_start=1800&year_end=2000&corpus=7&smoothing=3&share=&direct_url=t1%3B%2Clicence%20en%20lettres%3B%2Cc0%3B.t1%3B%2Clicence%20de%20lettres%3B%2Cc0) mais de
[licence **en** droit](https://books.google.com/ngrams/graph?content=licence+en+droit%2Clicence+de+droit&year_start=1800&year_end=2000&corpus=7&smoothing=3&share=&direct_url=t1%3B%2Clicence%20en%20droit%3B%2Cc0%3B.t1%3B%2Clicence%20de%20droit%3B%2Cc0) tandis que [l'histoire](https://books.google.com/ngrams/graph?content=licence+en+histoire%2Clicence+d%27histoire&year_start=1800&year_end=2000&corpus=7&smoothing=3&share=&direct_url=t1%3B%2Clicence%20en%20histoire%3B%2Cc0%3B.t1%3B%2Clicence%20d%20%27%20histoire%3B%2Cc0) et [la sociologie](https://books.google.com/ngrams/graph?content=licence+en+sociologie%2Clicence+de+sociologie&year_start=1800&year_end=2000&corpus=7&smoothing=3&share=&direct_url=t1%3B%2Clicence%20en%20sociologie%3B%2Cc0%3B.t1%3B%2Clicence%20de%20sociologie%3B%2Cc0) sont plus partagées. Pour la maîtrise, [<strong>d'</strong>histoire](https://books.google.com/ngrams/graph?content=ma%C3%AEtrise+en+histoire%2C+ma%C3%AEtrise+d%27histoire&year_start=1800&year_end=2000&corpus=7&smoothing=3&share=&direct_url=t1%3B%2Cma%C3%AEtrise%20en%20histoire%3B%2Cc0%3B.t1%3B%2Cma%C3%AEtrise%20d%20%27%20histoire%3B%2Cc0) l'emporte (et [**de** mathématiques](https://books.google.com/ngrams/graph?content=ma%C3%AEtrise+en+math%C3%A9matiques%2Cma%C3%AEtrise+de+math%C3%A9matiques&year_start=1800&year_end=2000&corpus=7&smoothing=3&share=&direct_url=t1%3B%2Cma%C3%AEtrise%20de%20math%C3%A9matiques%3B%2Cc0) encore plus) tandis que [**de** et **en** sociologie](https://books.google.com/ngrams/graph?content=ma%C3%AEtrise+en+sociologie%2Cma%C3%AEtrise+de+sociologie&year_start=1800&year_end=2000&corpus=7&smoothing=3&share=&direct_url=t1%3B%2Cma%C3%AEtrise%20en%20sociologie%3B%2Cc0%3B.t1%3B%2Cma%C3%AEtrise%20de%20sociologie%3B%2Cc0) restent partagés, tout comme l'est [le droit](https://books.google.com/ngrams/graph?content=ma%C3%AEtrise+en+droit%2Cma%C3%AEtrise+de+droit&year_start=1800&year_end=2000&corpus=7&smoothing=3&share=&direct_url=t1%3B%2Cma%C3%AEtrise%20en%20droit%3B%2Cc0%3B.t1%3B%2Cma%C3%AEtrise%20de%20droit%3B%2Cc0).

D'où vient cette différence ? Est-ce une spécificité du droit qui a déteint sur certaines sciences sociales ? Y a-t-il des variations régionales ?

<sub> (Question motivée par un point soulevé dans des commentaires sous [cette réponse](http://french.stackexchange.com/questions/5915/bachelor-degree-in-french/24509#24509)) </sub>