There are two basic ways to understand the prohibition of 'lifnei iver lo
sitayn michshol' (do not put a stumbling block before a blind person).
Rashi on this pasuk, as well as the Rambam and the Chinuch, explain it as
primarily a prohibition against being deceptive when giving advice to
those who are not in a strong position to know all the relevant facts. A
novice seeks expert advice about whether to invest in a particular deal.
The expert quickly understands it is a good deal in which to invest. He
tells the novice it is not a good deal, so that the novice won't invest
and the expert will be able to invest himself instead. Rashi explains that
the sense of the pasuk is don't put purposely bad advice (a stumbling
block) before a person who is ignorant (blind) as to this matter.
Others (SM"G and R' Saadia Gaon) explain it as primarily a prohibition
against enabling someone to do an aveira. One classic example is giving
wine to a nazir. [An interesting aside: It would seem that one difference
between the two approaches is whether someone who unsuccessfully seeks to
do the behavior in question has in fact transgressed the prohibition. If
the prohibition is against being deceptive, then the deception has
occurred whether or not the victim followed the bad advice; if the
prohibition is against leading someone to do an aveira, then giving a cup
of wine to a nazir is perhaps not prohibited (at least by virtue of lifnei
iver) unless the nazir actually drinks.]
No matter which way the mitzva is explained, the plain meaning of the
pasuk - causing a blind person to stumble - is definitely not the subject
of the prohibition. There are other prohibitions against this kind of
nasty behavior, but lifnei iver is not one of them. Why do we ignore the
plain meaning of the words in this pasuk? The Minchas Chinuch (Mitzva 232)
asks this question on the Chinuch and the Rambam. Given Rashi's reputation
for being the master of pshat (straightforward explanations), we can ask
this question of Rashi also. Why doesn't Rashi leave this pasuk alone -
why is any explanation needed?
I believe Rashi himself addresses this question at the end of the pasuk.
The pasuk finishes by saying 'v'yorayso may'elokecha ani hashem' (you
shall fear your L-rd, I am Hashem). Rashi here explains at length that the
expression of v'yorayso may'elokecha (fear your L-rd) is utilized when
dealing with an issue that cannot be discerned by other humans and only G-
d knows what really is happening. Applied to lifnei iver this means that
the expert may try to (falsely) explain away his behavior as an innocent
mistake ("I gave him the best advice I could"); to combat this the pasuk
says 'fear your L-rd', as HKB'H knows exactly what you were thinking.
Because the pasuk concludes with v'yorayso may'elokecha the earlier words
of lifnei iver must refer to something which is not obvious to other
people. If lifnei iver
means, literally, don't trip a blind person, there would be no need to say
v'yorayso may'elokecha because tripping a blind person can easily be
discerned by others.