Nedarim page 2. See Rav Shach Laws of Vows chapter 1. halacha 1.

To all Rishonim [authorities from the Middle Ages] except the Rambam, the main vow is by attaching the vow to a sacrifice. I.e., he says “This is forbidden to me like a sacrifice.” If he leaves out the words “like a sacrifice” it is still forbidden because of Yad leNeder (a handle on a vow). (A vow that wass not stated clearly and yet is still valid because of extension of the vow.) The opinion of the Ran however seems at first glance to be contradictory as to the point whether a vow needs to be attached to a sacrifice. Rav Shach explains that to the Ran (Rabainu Nisim ben Reuven), the main vow is without hatfasa (extension) [like the Rambam], but for it to be valid one needs the words “like a sacrifice.” Without those words, it sounds like he is saying something untrue, not that he is actively making something forbidden to himself. However, there is something here that seems difficult in this answer of Rav Shach. he says to the Ran the words like a sacrifice are for clarification, not because of a yad leneder. but I seem to recall that in one of the several places where the Ran brings his opinion, he does bring the idea of a Yad leNeder. [The places are in Nedraim page 2, top and bottom of the page, page 14 and in Shavuot. Later I saw that the place the Ran brings the idea of yad neder (lit. hand of a vow)]. Now onto a different point. The point of Rav Shach is that saying “this is forbidden to me” does not imply a neder but rather a statement that seems untrue. this is how he explains the Ran. However the same point ought to be applied to the Rambam. The Rambam says “the main vow is the statement ‘this is forbidden to me.’” This is valid not because of a yad, but for clarity, (but if he says like a sacrifice there is an added degree of stringency because then meila applies). However even without that still the main neder is the simple statement. but don’t we need to pronounce with one lips"? How could the Rambam escape from this conundrum>? ______________________________________________________________________________________________________ I see I wrote about this already but I think I ought to repeat the basic points in a clearer exposition. To all ראשונים except the רמב’’ם, the main vow is by attaching the vow to a sacrifice. I.e., he says “This is forbidden to me like a sacrifice.” If he leaves out the words “like a sacrifice” it is still forbidden because of יד לנדר (a handle on a vow). (A vow that was not stated clearly and yet is still valid because of extension of the vow.) The opinion of the ר''ן however seems at first glance to be contradictory as to the point whether a vow needs to be attached to a sacrifice. רב שך explains that to the ר''ן, the main vow is without התפסה (extension) [like the רמב’’ם], but for it to be valid one needs the words “like a sacrifice.” Without those words, it sounds like he is saying something untrue, not that he is actively making something forbidden to himself. However, there is something here that seems difficult in this answer of רב שך. He says to the ר''ן the words "like a sacrifice" are for clarification, not because of a יד לנדר. But I seem to recall that in one of the several places where the ר''ן brings his opinion, he does bring the idea of a יד לנדר. [The places are in נדרים page 2, top and bottom of the page, דף י''ד 14 and in שבועות]. Now onto a different point. The point of רב שך is that saying “this is forbidden to me” does not imply a נדר but rather a statement that seems untrue. this is how he explains the ר''ן. However the same point ought to be applied to the רמב’’ם. The רמב’’ם says “the main vow is the statement ‘this is forbidden to me.’” This is valid not because of a יד לנדר for clarity, (but if he says like a sacrifice there is an added degree of stringency because then מעילה applies). However, even without that, still the main נדר is the simple statement. but don’t we need to לבטא בשפתיים? How could the רמב’’ם escape from this conundrum?