Halakhah su Zevahim 6:9

But there is nothing that will clarify the difference between a negation and a prohibition to you besides the content of the statement. Indeed it will surely not be clarified by the word, for the word for negation and prohibition are the same in Hebrew; and that is the word, lo. So one learned must understand the content of the statement. And then he will quickly grasp which negative statement is a negation and which negative statement is a prohibition, according to our preceding explanation. And [the Sages], peace be upon them, already alluded to this matter. And that is in that which we find disagreement about a certain negative statement, as to whether it is a negation or a prohibition. And that is His saying regarding a bird sin-offering (Leviticus 5:8), "pinching its head at the nape, and he does not sever it." For behold our tanna - and that is the tanna that speaks in the mishnah (Zevachim 6:4) - holds that this is a prohibition; and therefore said that if he separated it, it is disqualified. And according to this, this negative statement would have to be a negative commandment. That is that if he severed it, it is disqualified - as if he brought leaven or honey [on the altar]. But Rabbi Elazar (ben Shimon) holds that this negative statement is a negation and not a prohibition; and that His saying, "he does not sever it," is intending to say, one does not have to sever the head, but rather one can cut it in any way that it might be. And hence - according to his opinion - if one severed it, it is [still] fit. And accordingly, they said in the Gemara, Zevachim (Zevachim 65b), "Rabbi Elazar ben Shimon would say, 'I have heard that we sever the bird sin-offering.' [Then] what is [the meaning of], 'he does not sever it?' He does not have to sever it." And they asked about this and said, "But from this - concerning a pit, about which it is written (Exodus 21:33), "and he does not cover it," is it also the same?" And the answer was, "There, it is written (Exodus 21:34), 'The one responsible for the pit must make restitution' - it is implied that he needs to cover it." Behold it has been clarified that they took a proof as to whether it is a negation or a prohibition from the content of the statement. And from it, it has become clear that His saying, "he does not sever it," is a negative commandment - according to what is written in the mishnah. And it has [also] become clear that His saying with a bird burnt-offering (Leviticus 1:17), "And he shall tear it open by its wings, he does not sever it," is inappropriate to count as a negative commandment - as it is a negation. And according to everyone, if he severs it, it is [still] fit. For it is because He said with an animal fire-offering (Leviticus 1:12), "And you shall cut it up into sections," that it would enter your mind that a bird burnt-offering is also like this. So He said that you do not need to sever it, but just tear it. So if he severed it, it is [still] fit - as is explained in its place.