A zucchini now is better than the possibility of a gourd later. There is no reason to give up an animal now for the hope of receiving another later.

MISHNA: It is written: ''He shall neither exchange it, nor substitute it, good for bad, or bad for good; and if he substitutes an animal for an animal, then both it and its substitute shall be sacred'' (Leviticus 27:10). The mishna enumerates the consecrated and non-sacred animals this verse applies to. One substitutes for consecrated animals from the flock of sheep or goats, and the sanctity takes effect upon animals from the herd of cattle, and one substitutes from the herd and the sanctity takes effect upon animals from the flock. And one substitutes from the sheep and the sanctity takes effect upon the goats, and from the goats upon the sheep; and from the males upon the females, and from the females upon the males; and from the unblemished animals upon the blemished animals, and from the blemished animals upon the unblemished animals.

The source for this is as it is stated: ''He shall neither exchange it, nor substitute it, good for bad, or bad for good'' (Leviticus 27:10). And which is the case of good for bad where the substitution takes effect? It is a case where one substitutes for blemished animals whose consecration preceded their blemish. But if an animal was consecrated after it was blemished, substitution for it does not take effect.

GEMARA: From where are these matters derived? They are derived from a verse, as the Sages taught in a baraita: The verse states: ''And if he substitutes an animal for an animal, then both it and its substitute shall be sacred'' (Leviticus 27:10). When the verse states: ''An animal for an animal,'' from here it is derived that one substitutes for consecrated animals from the flock and the sanctity takes effect upon animals from the herd, and one likewise substitutes from the herd upon animals from the flock; and one substitutes from the sheep and the sanctity takes effect upon the goats, and from the goats upon the sheep; and from the males upon the females and from the females upon the males; and from the blemished animals upon the unblemished animals and from the unblemished animals upon the blemished animals.

One might have thought that this is the halakha even for animals whose blemish preceded their consecration. Therefore, the verse states: ''He shall neither exchange it, nor substitute it, good for bad, or bad for good'' (Leviticus 27:10), and which is the case of good for bad where the substitution takes effect? It is a case of blemished animals whose consecration preceded their blemish. If an animal was consecrated after it was blemished, substitution for it does not take effect.

The Gemara discusses the second half of the baraita: What is the biblical derivation that leads to this conclusion? Abaye said that the verse should have stated: He shall neither exchange it, nor substitute it, good for bad, or bad for it. Why do I need another instance of the term ''for good''? Learn from this repetition that if the animal is good, i.e., unblemished, from its beginning, before it was consecrated, one can render a substitute for it, but if it is bad from its beginning, one cannot render a substitute for it.

Rava said: Both instances of the word ''good'' in the verse are superfluous. If so, let the verse write: He shall neither exchange it, nor substitute it for bad, or bad for it. Why do I need the verse to write both instances of the word ''good''? One instance of the word ''good'' teaches that even if one substitutes a good animal for a good animal, when he effects substitution he is flogged. And the other instance teaches that if the animal is good from its beginning one can render a substitute for it, but if it is bad from its beginning one cannot render a substitute for it.

And Abaye said: The first derivation of Rava is unnecessary, as that halakha is already derived by an a fortiori inference, as follows: Just as one who substitutes a good animal for a bad blemished one, where he seeks to improve the standing of the consecrated animal by making it fit for sacrifice, is nevertheless flogged, is it not all the more so the case that one who substitutes a good animal for a good animal, which are equivalent to each other, should be flogged?

And Rava would respond that an a fortiori inference is not sufficient, as one does not administer punishment based on an a fortiori inference. Punishment with lashes can be based only on the explicit wording of a verse. And Abaye could say to you that this is not a mere logical derivation, but it is included in the language of the verse, as, is substituting a good, unblemished, animal less of an act of substitution than substituting a bad one? The prohibition stated in the verse clearly applies in either case.

§ The Sages taught in a baraita that when the verse states: ''He shall neither exchange it,'' this is referring to substituting one’s animal for that of others. The phrase ''nor substitute it'' is referring to substituting one’s non-sacred animal for his own sacred one. The Gemara objects: But let the verse write simply: ''He shall not exchange it,'' and there will be no need to write: ''Nor substitute it,'' as the prohibition against substituting for one’s own animal can be inferred a fortiori from the prohibition against substituting for another’s animal.

The Gemara explains: If the verse had written the prohibition in that manner, I would say that one is flogged only if he stated: This consecrated animal should leave its consecrated status and this non-sacred animal should enter in its stead. But if one effects substitution by simply stating: This is a substitute for that, as he has consecrated both of the animals, I would say that he is not flogged. The additional phrase in the verse teaches us that he is flogged in this case as well.

The Gemara explains: What are the circumstances of substituting his animal for that of others? If we say that the consecrated animal is his and the non-sacred animal belongs to others, is he able to consecrate an animal in this manner? The Merciful One states in the Torah: ''When a man shall consecrate his house to be sacred unto the Lord'' (Leviticus 27:14), which teaches that just as his house is in his possession, so too, any item one desires to consecrate must be in his possession. One cannot consecrate another’s animal. But rather, if we say that the consecrated animal belongs to others, and the non-sacred animal is his, can one effect substitution for an item that is not his?

The Gemara explains: Actually, the baraita is referring to a consecrated animal of others and his non-sacred animal, and it is a case where the owner of the consecrated animal said that whoever wants to effect substitution for his animal can come and effect substitution. In this case, one can effect substitution even for a consecrated item that is not his.

MISHNA: One substitutes one non-sacred animal for two consecrated animals and two non-sacred animals for one consecrated animal, and one substitutes one non-sacred animal for one hundred consecrated animals and one hundred non-sacred animals for one consecrated animal. Rabbi Shimon says: One substitutes only one non-sacred animal for one consecrated animal, as it is stated: ''Then both it and its substitute shall be sacred'' (Leviticus 27:10). Just as ''it'' indicates one specific animal, so too, its substitute can be only one specific animal.

GEMARA: With regard to the dispute between the first tanna and Rabbi Shimon, the Gemara explains: From where are these matters derived? As the Sages taught in a baraita: The verse states: ''An animal for an animal'' (Leviticus 27:10). From here it is derived that one substitutes one non-sacred animal for two consecrated animals and two non-sacred animals for one consecrated animal, and one non-sacred animal for one hundred consecrated animals and one hundred non-sacred animals for one consecrated animal. Rabbi Shimon says: One substitutes only one non-sacred animal for one consecrated animal, as it is stated: ''An animal [behema] for an animal,'' and it is not stated: An animal for animals [bivehemot], nor: Animals for an animal.

The first tanna said to Rabbi Shimon: We have found that a group of animals is called by the singular term behema, as it is stated: ''And many animals [uvhema rabba]'' (Jonah 4:11). The Gemara notes: And Rabbi Shimon could respond that many animals are indeed called ''behema rabba,'' but they are not called ''behema'' without further specification.

The Gemara asks: And is the reason of Rabbi Shimon really due to the verse’s phrase ''an animal for an animal''? But isn’t the reason of Rabbi Shimon, as explained in the mishna, due to the word ''it'' in the verse? Just as ''it'' indicates one specific animal, so too, its substitute can be only one specific animal.

The Gemara answers: Initially, Rabbi Shimon stated his opinion to the Sages by drawing support from the phrase: ''Then both it and its substitute.'' But when he saw that the Rabbis taught their opinion drawing support from the phrase ''an animal for an animal,'' he said to them: You can learn the reason for my opinion from there too.

Reish Lakish says: Although he holds that one cannot substitute two animals for one, Rabbi Shimon concedes that one can effect substitution once and then effect substitution again for the same consecrated animal. What is the reason for this? The reason is that one can ask: Where has the initial consecration of the consecrated animal gone? Even after one effects substitution, it remains consecrated as it was before. And Rabbi Yoḥanan says: Rabbi Shimon maintains that just as one cannot substitute two animals for one, so too, one cannot effect substitution and then effect substitution again using the same consecrated animal.

The Gemara comments: It is taught in a baraita in accordance with the opinion of Rabbi Yoḥanan, and it is taught in a baraita in accordance with the opinion of Reish Lakish. It is taught in a baraita in accordance with the opinion of Rabbi Yoḥanan: Just as one cannot substitute one animal for two, so too, one cannot effect substitution and then effect substitution again. It is taught in a baraita in accordance with the opinion of Reish Lakish: One might have thought that just as Rabbi Shimon said that one cannot substitute two animals for one, so too, one cannot effect substitution and then effect substitution again. Therefore, the verse states: ''Then both it and its substitute'' (Leviticus 27:10), which teaches that one can effect substitution with even one hundred non-sacred animals.

Rabbi Avin raises a dilemma: According to the statement of the one who says that one cannot effect substitution once and then effect substitution again, if one designated an animal as a guilt offering with which to atone and effected substitution for it,