The אבני מילואים in שו"ת סימן כ"ב brings a famous and fundamental מחלוקת אחרונים from the מהרי"ט as to how to understand how נזירות works. The question is: is נזירות an איסור חפצא or איסור גברא? If it is an איסור גברא then it would be similar to a שבועה which is on the person themselves. If it is an איסור חפצא then it would be like a נדר where the item itself is אסור but not the person. I think most of us would have intuitively assumed it was an איסור גברא. The person is declaring themselves a נזיר which means they will not drink wine, cut their hair, or be מטמא למיתים. To suggest otherwise sounds like you are saying that when a person declares himself a נזיר, he is really saying he is making the wine itself אסור on him, his hair אסור in relation to cutting it, and the dead man is אסור in relation to being in its presence or touching it. The מהרי"ן לב holds it is an איסור חפצא. His proof is the following: The רי"ף in שבועות says that if you make a שבועה not to eat meat, and then you decide you don’t want to eat bread either and you say on a piece of bread “this bread should on me like meat”, it doesn’t work. Similarly, if you hear your fried make a שבועה not to eat meat and you say “me too”, it doesn’t work. However, by נדרים it works as we know that if a person says “I’m a נזיר” and his friend hears him and says “me too”, he is a נזיר. From that רי"ף it seems clear it is an איסור חפצא like נדרים. The ריטב"א is נדרים דף י"ח is also of the opinion that its an איסור חפצא. However, the מהר"י באסאן argues and says it is an איסור גברא, but not for the reason you might think. He actually starts saying it is an איסור חפצא and explains the way you would say it is that by saying “I am a נזיר” you are really saying “my lips should be אסור for drinking wine, my legs for walking into cemeteries, and may hair for cutting”. However, since most of your limbs get included it’s really similar to an איסור גברא. The מהרי"ט himself has third option that it is neither an איסור חפצא nor anאיסור גברא. Rather, the person who says he is a נזיר is declaring himself to be a קדוש. It’s almost like being מקדיש yourself to קדושת כהונה. Therefore, once you are a נזיר, the Torah has three new restrictions for you. So it is not that you made yourself אסור on these things. Rather, by declaring yourself a נזיר the Torah made these things אסור on you like a כהן has special איסורים. The אבני מילואים who brought this מחלוקת wanted to use it to explain the following: would you call נזירות an איסור השוה בכל or not? תוספות on דף מ"א ע"ב in ד"ה ואי seems to hold it’s a מחלוקת הסוגיות where the גמרא on דף נ"ח calls it a לאו ּהשוה בכל, yet elsewhere the גמרא seems to hold it isn’t שוה בכל. He suggests it should be תלוי on this discussion. If you hold it is an איסור גברא or even an איסור חפצא then it should be שוה בכל as any man or woman can become a נזיר. However, if it’s an איסור תורה that was put on you by becoming a נזיר, then it would be similar to איסורי כהנוה which are not considered שוה בכל. What’s interesting is that the מדרש רבה in נשא פּרשה י אות י"אseems to make a split. It says that someone who makes themselves a נזיר by being מקדש himself מלמטה, Hashem is מקדש him מלמעלה. Therefore, since the person was מצער himself from wine and cutting his hair, the Torah makes him like a כהן and he cant be מטמא למיתים. That sounds like the איסור יין ותגלחת are an איסור גברא or איסור חפצא, but the איסור טומאה is an איסור תורה.