There is a matter of dispute among the Rishonim if the prohibition against performing labor on Chol Hamoed (the intermediate days of Pesach and Sukkos) is Biblical (Rashi) or Rabbinic (Tosfos).
Our Gemora cites Scriptural verses illustrating that it is forbidden to perform labor during Chol Hamoed. Tosfos states that it is implicit from the Gemora that this is a Biblical prohibition.
Tosfos asks: It is permitted to work on Chol Hamoed to prevent an irretrievable loss or various types of labor; this would be understandable if the prohibition would be Rabbinic in nature, however, if it is a Biblical prohibition, where do we find distinctions in the types of work that some will be forbidden and some will be permitted?
Tosfos concludes that the prohibition against working during Chol Hamoed is only a Rabbinic injunction and the verses cited are merely Scriptural supports for this decree.
Tosfos asks from a Gemora in Avodah Zarah (22a) which states that there would be a prohibition of placing a stumbling block before a blind man (lifnei iver) by performing labor on Chol Hamoed. (One is forbidden from assisting another fellow to violate a prohibition, where the sinner could not accomplish the transgression without his aid.)
The Reshash explains Tosfos: The prohibition of lifnei iver is only applicable by a Biblical prohibition and not when it pertains to a Rabbinical injunction; accordingly, Tosfos asks why the Gemora states that lifnei iver applies by the prohibition of working on Chol Hamoed, when that is only a Rabbinic injunction.
Tosfos in Avodah Zarah (22a) states explicitly that the commandment of lifnei iver applies by a Rabbinic prohibition, as well. The Steipler Gaon explains a different Tosfos (Avodah Zarah 15b) that Tosfos is uncertain regarding this principle and it is indeed a dispute among two answers in Tosfos if lifnei iver applies by a Rabbinic prohibition or not.
This principle requires an explanation. Why should lifnei iver not apply by a Rabbinic prohibition? One is forbidden from providing flawed advice to his fellow (the Minchas Chinuch discusses if giving shoddy counsel violates this prohibition); every Rabbinic decree entails a Biblical prohibition of not swaying from the words of our sages.
What is the logic to differentiate between assisting someone to violate a Biblical prohibition or one that is merely Rabbinic?
avrohom adler, usa
Tosfos' case involves selling a field to a Jew who will till it on Chol ha'Mo'ed, because he does not accept the Halachah that prohibits doing so.
Allowing a person to sin by giving him a field is not really comparable to tripping a blind man, since the decision to work on Chol ha'Mo'ed lies entirely with the one who gets the field. He sins of his own volition.
Nevertheless, it is included in the prohibition since when the sinner sins, he causes permanent, spiritual damage to himself (barring an act of Teshuvah) via the field. The damage that is caused is not the sin - which was the choice of the sinner - but what he suffers afterwards due to the spiritual damage my field brought him by being plowed on Chol ha'Mo'ed.
An act prohibited by the Rabanim, though, is not inherently damaging to the soul. What damages the sinner is the fact that he did not heed the Rabanan. This is not a damage the field is doing, so the owner of the field does not transgress Lifnei Iver.
(A similar argument applies when one causes another Jew to unwittingly transgress a Rabbinic or Torah prohibition.)
Best wishes,
Mordecai Kornfeld
Kollel Iyun Hadaf
A few comments on your answer:
(a) Quote: A similar argument applies when one causes another Jew to unwittingly transgress a Rabbinic or Torah prohibition.)
Do you mean that if one causes a Jew to unwittingly trasgress, there is no lifnei iver on the etzem aveira, but rather on the spiritual damage done?But isn't causing the person to sin b'shogeg precisely similar to tripping a blind man?Is there then no case of being machshil someone that is analagous to tripping a blind man?
I assume that what you mean is that there cant be lifnei ever on the shogeg since its not an aveira, certainly when its on a d'rabbanan (nesivos) and its only the spiritual damage - im not sure if thats akin to tripping the blind man, which would be comparable to the etzem aveira.
(b) Quote "A similar argument applies when one causes another Jew to unwittingly transgress a Rabbinic or Torah prohibition"
I think a proof that casing a Jew to do a Doraisa B'Shogeg is Lifnai Iver is Tosfos Avoda Zara 7b D"H Minayin that the reason you can't pass wine top a Nazir is because it's not something he's used to and he might forget and drink it. We don't worry usually about passing Issurim to regular Jews.
(c) Another comment:
Quote "An act prohibited by the Rabanim, though, is not inherently damaging to the soul. What damages the sinner is the fact that he did not heed the Rabanan. This is not a damage the field is doing, so the owner of the field does not transgress Lifnei Iver."
I find this to be Dakusdik and cannot understand why would this change the situation. If someone's not heeding the Rabanan is manifested by working the field, then the field is causing him the spiritual damage. It would be like saying that you may give a Nazir wine, since the drinking the wine is not really the prohibition, but rather keeping his word.
If you meant that there is a difference between an Issur Gavra and an Issur Cheftza, I don't see why work on Chol Hamoed is more an Issur Cheftza, it would seem that it's more an Issur Gavra not to do Malachos rather than the field being something that you can't work with.
Avrohom Adler, Cleveland OH
(a) You are correct.
The case of causing a person to sin which is indeed similar to tripping a blind man - or better yet, is similar to giving a person bad advice - is the case that the Toras Kohanim itself gives when defining Lifnei Iver: Telling a Kohen he is permitted to marry a Gerushah. Misinforming someone about a Mitzvah is equivalent to misinforming him about a business deal. Not so, when a person either gives an object to his friend which his friend chooses on his own to use for an Aveirah, or when a person feeds something that is Asur to his friend, causing his friend to unwittingly commit the Aveirah. (The latter is not even Shogeg - it is Mis'asek.)
(b) That is correct. In fact, we find often that causing someone to unwittingly eat a forbidden food is Lifnei Iver. One example involves Kutim, who tell us that they took off Ma'aser even though they didn't since they do not keep the Mitzvah of Lifnei Iver (Eruvin 37b etc.)
What I meant by the parenthetical statement is that the dichotomy between d'Oraisa and d'Rabanan exists whether one lends an object to his friend which his friend chooses on his own to use for an Aveirah, or whether one gives his friend something that is Asur which his friend unwittingly uses or eats.
(c) As you are certainly aware, the Minchas Chinuch asks your question and cites all of the references that you provided (Mitzvos #232:3, #343:4 - in the Mechon Yerushalayim edition), see also Pardes Yosef (Vayikra 19:14 and Bereishis ). They provide no answer to the question.
Allow me to explain my answer more clearly (with help from my son Yisrael): Lifnei Iver only applies when the sinner could not have committed the sin in question without the help of the "Machshil". This is called "Trei Evrei d'Nahara" (Avodah Zarah 6b). If a person does not have a field, he cannot transgress the Isur of working his field on Chol ha'Moed. Therefore, if work on Chol ha'Moed is prohibited by the Torah, by selling such a person a field I am allowing him to transgress a prohibition that he otherwise would not be able to transgress. This is Lifnei Iver.
However, if work on Chol ha'Moed is only prohibited by the Rabanan, the transgression is not "working a field", but rather "disregarding the words of the Rabanan." Even a person without a field can disregard the words of the Rabanan in many other ways. Therefore, by selling such a person a field I have not helped him transgress a prohibition that he otherwise would not transgress. That is why this is not Lifnei Iver.
(This applies to the first of the two scenarios of Lifnei Iver that I mentioned above (b). In the second case (i.e. causing a person to unwittingly sin), there is no Lifnei Iver by a d'Rabanan either for the reason I mentioned in my first communication, or because no Isur is done when a person transgresses a d'Rabanan b'Shogeg - the Nesivos you alluded to.)
For a beautiful discussion of the difference I pointed out between the transgression of a Rabbinic law (disobeying the Rabanan) and a Torah law (where the act itself is prohibited) see Meshech Chochmah, Devarim 17:11.
(d) The truth is, though, that Tosfos probably understood (for the reasons mentioned above, (a)) that causing a person to sin is not included the simple meaning of the verse Lifnei Iver. Rather, it is included in the prohibition based on some Ribuy (perhaps the word "Lifnei"). This inferred Isur Torah may be limited to causing someone to transgress a Torah prohibition, but will not include causing someone to transgress a Rabanan prohibition. (The Rabanan may not have instituted k'Ein d'Oraisa here for a number of reasons.)
Best wishes,
Mordecai Kornfeld