We learned that if one didn't make an eruv tavshilin beforehand he is unable to make deception/ploy/subterfuse/cheat to eat what he cooks because he will not do tshuvah, thinking its ok & will fool himself& can fool others into sinning. it is more stringent than someone who transgresses openly because nobody will learn from them. So we see here that we are very strict , moreso with deceivers than with open transgressers, fine. Thn when I try to investigate the halacha further, everyone seems to say that one can deceive & cook on YOM TOV for Shabbos if he hadn't made the eruv by cooking many different kinds of foods that he knows he won't eat all of on YOM TOV & they are really for Sabbos. He can do this as long as he at least eats a little from each of the foods on YOM TOV. Isn't this deception as well & why is it permitted?
yehoshua yosef fox, BKLYN, USA
We indeed allow deceptions that are not obvious if one did not make an Eruv Tavshilin (see Shulchan Aruch 527:21 and Mishnah Berurah 527:70,71). This is because the prohibition of such cooking on Yom Tov is a Rabbinic decree (when there is time to eat the food on Yom Tov and one's intent is to eat some of it on Yom Tov). Being that the lack of food will severely hamper one's Yom Tov, the Rabbanan allowed deceptions that are not obvious to circumvent this decree, such as the one you mentioned in the last half of your question. However, obvious deception, such as cooking normally for Shabbos without intent to eat any of it on Yom Tov, is indeed prohibited and is a serious transgression.
All the best,
Yaakov Montrose