Nature Of Chermei Kohanim

(18:14) כׇּל־חֵ֥רֶם בְּיִשְׂרָאֵ֖ל לְךָ֥ יִהְיֶֽה.  The Gemorah in Bechorot 32a (cited in Torah Temimah) says תניא, החרמים כל זמן שהן בבית בעלים הרי הן כהקדש לכל דבריהם, שנאמר (פ׳ בחקתי) כל חרם קודש קדשים הוא לה׳, נתנן לכהן, הרי הן כחולין לכל דבריהם, שנאמר כל חרם בישראל לך יהיה.  There are two ways that one can understand this law.  One way to view it is the person is doing an act of making something hekdesh and the kohanim are given the rights to obtain the object from hekdesh.  Another possibility is that the person is giving a gift to the kohan but the Torah gives it the laws of hekdesh as long as it hasn’t been given over to the kohan.  This would seem to be the doubt of the Minchas Chinuch #357 if gentiles or a מופלא הסמוך לאיש that have the ability to make something hekdesh would be included in this din.  According to the first approach their hekdesh will be valid for it is within their capability to make something hekdesh.  However, according to the second approach that the kedusha is a special din that the Torah superimposes, that is only said regarding Jews that are of age.  This debate of the Minchas Chinuch is already explicit in the Sifri (18:4) that includes gentiles to the law of cherem based on the words כל חרם but some texts have that it is only including גרים (see meforshim.)

The Rosh in Nedarim holds that חרמי כהנים are considered to be a דבר הנדור.  That understanding only makes sense if you assume the person is doing the act of the hekdesh.  However, ר"א מן ההר disagrees with him, he would hold the hekdesh is superimposed by the Torah.

Another difference these two ways of understanding would make is if there should be a din of אמירה לגבוה כמסירה להדיוט regarding חרמי כהנים.  Tosfos Temurah 32b and Sfas Emes there debate this point (see Toras Hakodesh volume 3 siman 13 for further discussion.)