Halakhah su Levitico 11:24

That is that He commanded us that when any person touches a carcass, he becomes impure. And this commandment includes the impurity of a carcass and all of its laws. And I will now present a preface that is appropriate that we remember anytime we mention the various types of impurity. And it is that that which we count each type as a positive commandment - its content is not that we are obligated to become impure with a certain impurity, and also not that we are prohibited from becoming impure from it and that it be a negative commandment. Rather the Torah said that anyone who touches this type [of object] becomes impure; or that this thing renders one who touches it impure according to this description. And that is the positive commandment - meaning that this law with which we have been commanded is a positive commandment. And that is His saying, whoever touches this according to this description has become impure; and whoever according to that description does not become impure. But the matter itself is optional - if he wants, he becomes impure; if not, he doesn't become impure. And the language of the Sifra (Sifra, Shemini, Chapter 4:10) is, "'And their carcass do not touch' (Leviticus 11:8) - I might think that if one touched a carcass, he receives lashes. [Hence] we learn to say, 'and to these you shall become impure' (Leviticus 11:24). I might [then] think that if one saw a carcass, he should go and become impure from it. [Hence] we learn to say, 'and their carcass do not touch.' How is this? You shall say, it is an option." And this commandment that has been told to us about this law - that one who touches this become impure; and that he will be impure, such that he will be obligated about everything that impure people are obligated, [such as] to exit from the camp of the Divine Presence, not to eat consecrated food, not to touch it and other things besides this - this is the command. That means to say, one becoming impure from this type when he touches it or was proximate to [it] in such a manner. And remember this matter with every one of the types of impurity. (See Parashat Shemini; Mishneh Torah, Other Sources of Defilement 1.)

The commandment of the matter of the impurity of a carcass: That a carcass be impure and render impure, as it is stated (Leviticus 11:39), "And if a beast dies that is for you to eat, etc." Rambam, may his memory be blessed, wrote about this commandment (Sefer HaMitzvot LaRambam, Mitzvot Ase 96), and this is his language: "And I will mention to you here now a nice preface, that you should remember about all that we mention of the types of impurities. And it is that that which we count each and every type of the impurities as a positive commandment, its substance is not that we would be obligated to become impure with this impurity, and likewise not that we are prevented from becoming impure from it and that is should be a negative commandment. However since the Torah states that one who approaches this species is impure or that this thing becomes impure in this way by the one who approaches it, that is a positive commandment - meaning to say that this law that we are commanded about is a commandment. And that [commandment] is that which we said, that the one who approaches such in this way becomes impure, and the one in that way does not become impure. And as to one becoming impure, himself, the option is in the hand of each man: As if he wants, he becomes impure; and if he wants, he does not become impure. And the language of Sifra, Shemini, Chapter 4:10 is '"And their carcass you shall not touch" - it is possible that if one touched a carcass he receives forty stripes; [hence] we learn to say "and to these you shall become impure" (Leviticus 11:24). It is possible that if one saw a carcass, he should go and become impure from it; [hence] we learn to say "their carcass you shall not touch." How is this? I would say [it is an] option.' And the commandment is that which is said to us about these laws - that the one who approaches this becomes impure and will be impure; and he will be obligated that which the impure are obligated - to go out of the encampment of the Divine Presence and not to eat from the holy, and not come close to it and other than this. And that is the commandment, meaning to say his being impure with this species, when he approaches it or be with it in this manner. And remember this matter with each and every type of impurity." To here is his language. And with all of this, it does not sit well with the heart for us to think of this matter as a commandment. And nonetheless we shall not veer from the path of our rabbi in our tally to the right or the left, as we set out at the beginning.