In the (second presentation of the) tenth commandment (Deut 5:17), why does the Torah use two different words in Hebrew (תחמד and תתאוה) that mean almost the same thing is English ("covet" or "desire"). I can find no explanation in Rashi. What is the difference between those words?
לא תתאוה refers simply to having a desire.
לא תחמד refers to not only desiring someone's stuff but acting on that desire to actually get it.
If one takes it from him forcefully, he's violated the third aveirah of לא תגזול.
And if he's not careful and lets his desire for the property get away from him, he might c"v end up violating לא תרצח as well.
Thus says the Shulchan Aruch (CM 360:12). He, in turn, got it from the Rambam (Hilchos Gezeilah 1:12). This is how the Sefer HaChinuch (Mitzvah 416) interprets the difference as well.
It's noteworthy that Rashi (Devarim 5:18) holds that there is absolutely no difference between לא תתאוה and לא תחמד, with a prooftext from Onklos in Parshas Bereishis. I'm not sure why he doesn't agree with the Poskim, who seem to have the Gemara on their side (BM 6a, which talks about the issur of לא תחמד, doesn't mention לא תתאוה even once).
@DanF pointed out that the two terms seem to be used differently in different contexts. Specifically the following pesukim:
לא תחמד בית רעך לא תחמד אשת רעך ועבדו ואמתו ושורו וחמרו וכל אשר לרעך - שמות כ:יד
לא תחמד אשת רעך ולא תתאוה בית רעך שדהו ועבדו ואמתו שורו וחמרו וכל אשר לרעך - דברים ה:יח
פסילי אלהיהם תשרפון באש לא תחמד כסף וזהב עליהם ולקחת לך פן תוקש בו כי תועבת ה׳ אלקיך הוא - דברים ז:כה
So we see that לא תתאוה is used in respect to immovable property, slaves, and animals, while לא תחמד is more broadly applied to not only immovable and movable property, but also one's wife. Why?
Also notice the third aveirah in this triplet: לא תגזל. Ignoring the instances in which it refers to kidnaping, the word is always used in respect to movable property:
כי יגנב איש שור או שה וטבחו או מכרו וגו׳ - שמות כא:לז
ואם גנב יגנב מעמו ישלם לבעליו -שמות כב:יא
נפש כי תחטא ומעלה מעל בה׳ וכחש בעמיתו בפקדון או בתשומת יד או בגזל או עשק את עמיתו. או מצא אבדה וכחש בה וגו׳ והיה כי יחטא ואשם והשיב את הגזלה אשר גזל וגו׳ - ויקרא ה:יח-כד
לא תעשק את רעך ולא תגזל לא תלין פעלת שכיר אתך עד בקר - ויקרא יט:יג
I'm assuming that לא תתאוה isn't used in respect to one's wife because that's already covered under לא תתורו אחרי לבבכם ואחרי עיניכם אשר אתם זנים אחריהם. Getting that out of the way, notice that stealing is always used in respect to movable property while לא תתאוה and לא תחמד are both used in respect to immovable property as well. This is because it's impossible to steal land (Sukkah 31a).
Very thorough and interesting answer. I think it can be improved if you can explain why לא תחמד is said regarding only the neighbor's wife while לא תתאוה is said regarding the neighbor's field, house, etc. I would think that לא תתאוה should apply to his neighbor's wife as well. He should be desiring only his own wife.– DanFAug 24, 2016 at 18:16
@DanF Touched on that a bit, and expanded on the difference between those two and לא תגזול.– DonielFAug 24, 2016 at 20:19
Rashi could be explaining the Peshat, whereas the Gemara is giving a Midrash Halakha.– Double AA ♦Aug 24, 2016 at 20:26
@DoubleAA Maybe. But Rashi knew the Gemara, and he seems in general to be picky on the differences between shorashim. I'm curious why he ignored it.– DonielFAug 24, 2016 at 20:33
There's also התאוו תאוה Num 11 for that Shoresh.– Double AA ♦Aug 24, 2016 at 20:37
There are at least two opinions that differentiate halachically between the two terms:
The Rambam in M.T. (Gzeilah 1:9-10) and Shulchan Aruch (C.M. 359) hold that לא תתאוה refers to plotting to acquire the coveted item, while לא תחמד refers to actually pressuring the owner into giving it to him.
The Sefer Hachinuch (417) (and perhaps the Rambam in Sefer Hamitzvos L.S. 266) hold that לא תתאוה refers even to mere desire.
It is important to note that (in light of the above ruling of the Shulchan Aruch), contrary to popular belief, it is not forbidden to feel envious of someone else's possessions, as long as you don't begin to think about how you can get them from him.