Orlah, Chapter Two, Mishnah 10. This mishnah addresses the question of whether different prohibitions combine with one another to create a prohibition. The case involves spices and seasonings that carry two or three types of prohibitions, and the question is whether they can be joined together to make up a single measure of forbidden food.
The two cases in the mishnah:
Different names from one species: Two or three spices that are all one species - all pepper, for example - except that each one is forbidden on account of a different prohibition: one is kilei hakerem (mixed seeds in a vineyard), the second is orlah, and the third is Terumah (for someone who is not a kohen).
Different species with one name: Three different kinds of spice - pepper, onion and vinegar - but all of them are forbidden on account of a single prohibition, kilei hakerem, for example.
In both cases the mishnah rules: "asur u'mitztarfin" - even though they are not one species, or their prohibition does not stem from one name, they nevertheless combine with one another to create the prohibition.
The view of Rabbi Shimon:
Rabbi Shimon disagrees and holds that "einan mitztarfin" - they do not combine: neither in the case of two or three names from one species, nor in the case of two species with one name do the prohibitions join together.
Therefore, according to Rabbi Shimon, there is no prohibition unless there is a sufficient measure in one of the spices on its own, meaning that its taste is discernible by itself and does not need the other spices added to it in order to be noticeable. But if the taste of the forbidden food is discernible only through combining them together, that is not enough to create a prohibition.
In summary: The Tannaim disagree about combining different prohibitions - both in the case of spices of one species whose prohibitions differ, and in the case of different species that share one prohibition. According to the Sages, "asur u'mitztarfin" - they are forbidden and they combine; according to Rabbi Shimon, "einan mitztarfin" - they do not combine, and there is no prohibition unless the taste of one of the spices is discernible on its own without the others being added to it.