Is lying per se forbidden? If not, are there circumstances under which (certain lies) are forbidden? On what grounds?
What about:
If you have a good enough reason to lie (e.g. for the sake of a mitzvah -- For example, could I say I was sick so as not to shake someone's hand?) -- or generally to avoid harm?
If the addressee were a minor?
If the addressee were not Jewish?
See Gemara BM 23b
For Rab Judah said in the name of Samuel:What is the point [in this observation]? - Mar Zutra said: [It is important in regard to the question] of returning a lost article, [recognised] by sight: If we know that [the claimant] conceals the truth those three matters only we give it back to him, but if he does not speak the truth also in other matters we do not give it back to him.
In the following three matters learned men do conceal the truth:
- In matters of a tractate {they ask know you this Massechet at your fingertip and by humility he says "No!" (Rashi)},
- bed {If they ask if he has a sexuel intercourse, he can hive a negative answer, even if it is not true, by modesty (adapted from Rashi), If he comes later to the study because of Tevilat Ezra, he can give a false explanation to his delay},
- hospitality {If they ask about the quality of the accomodation provided by its host, he can protect him against a large inflow of profiteers (adapted from Rashi)}.
See Yevamot 65b:
- Rabbi Ile'a further stated in the name of Rabbi Eleazar son of Rabbi Simeon: One may modify a statement in the interests of peace; for it is said in Scripture, Thy father did command etc. so shall ye say unto Joseph: Forgive, I pray thee now, etc.{Yaakov do not order but they change in the interest of peace (Rashi)}
- Rabbi Nathan said: It is a commandment; for it is stated in Scripture, And Samuel said: 'How can I go? If Saul hear it, he will kill me', etc. {G_d commanded him to change and to take a calf and to lie}
- At the School of Rabbi Ishmael it was taught: Great is the cause of peace. Seeing that for its sake even the Ho One, blessed be He, modified a statement; for at first it is written, My lord being old, while afterwards it is written, And I am old. {Sarah spoken with disdain about Avraham}
The first Gemara enumerates current situations, the third case is also for reason of peace. The second Gemara gives examples of great people and G_d itself. You can see two examples of harm (Shmuel, see Nazir chapter 9, Mishna 5 "אָמַר לוֹ רַבִּי נְהוֹרַאי, וַהֲלֹא כְבָר נֶאֱמַר (שמואל א טז) וַיֹּאמֶר שְׁמוּאֵל אֵיךְ אֵלֵךְ וְשָׁמַע שָׁאוּל וַהֲרָגָנִי, שֶׁכְּבָר הָיָה עָלָיו מוֹרָה שֶׁל בָּשָׂר וָדָם", R Nehorai said to him: but does it not also say, and samuel said; 'how can i go? if Saul hear it he will kill me' [which shows] that he was in fact afraid of a human being?)
Generally, you should not lie. Sotah 42a makes it clear that those who lie (shakranim) do not merit the divine presence. Who are these shakranim? dafyomi.co.il translates it as follows:
SHAKRANIM (9 categories):
(a) One who lies in order to steal from or abuse others, thereby transgressing the prohibitions of "Lo Sigzol" and "Lo Soneh."
(b) One who lies in order to present himself as someone's friend so that at some point in the future he will be able to steal from him or swindle him.
(c) One who lies in order to receive some future benefit that he would not have received otherwise.
(d) One who lies (even though he causes no harm) simply because he is accustomed to lying, or because he does not clarify the facts before he repeats them. (This is permitted "Mipnei ha'Shalom," for the sake of peace; see Insights to Yevamos 65b.)
(e) One who acts towards others differently than the way he feels inside, even though he does not openly lie.
(f) One who promises to give something to (or do something for) his friend and does not fulfill his promise. If he offers his friend something small or easy, even if he does not make a promise to give it he still must keep his word.
(g) One who tells others about the way he helped someone else, when he really did not help (Geneivas Da'as).
(h) One who praises himself, or accepts praise, for good traits that he does not possess.
(i) A person who occasionally lies regarding issues that in no way affect others, but merely because he derives benefit (such as attention) from his lies.
So let it be clear that telling lies is not a positive habit to get into. But this is not the whole story. There are several instances in the Torah where 'little white lies' were told in pursuit of peace. The two most recognizable instances are: -When G'd subtly rewords Sarah's reaction to Abraham (he changes the part where she sais that her husband is old) (bereishit 18:12 versus 18:13). -When Josephs brothers tell Joseph that their father Ja'akov had sent them.
There is much to be said, but the article on chabad.org seems to give a nice overview and also makes it clear that to outright lie (as in spreading falsehoods) is not permitted, but slightly changing the truth for the sake of peace can sometimes be condoned, but never to be taken lightly.
One may "change the truth" for reasons of peace. We derive this from a conversation between G‑d, Sarah and Abraham in Genesis.17 Sarah said to herself: "After I have withered will I get smooth skin, and my husband is old." When G‑d repeated her comments to Abraham, he said that Sarah had said: "How can I give birth when I am old." As Rashi explains, G‑d changed Sarah's words so that Abraham would not realize that Sarah had made a denigrating remark about him.
Summarising the article continues:
Other examples of permitted white lies include:
Changing the truth in order to practice humility. [...]
Changing the truth in order to maintain modesty.
Changing the truth in order to protect someone else from harm or inconvenience [...]
A white lie said in order to protect someone from embarrassment. [...]
Using exaggerated expressions if it is clear that it's an exaggeration.[...]
There are some circumstances under which one is allowed to be deceptive in order to recoup losses that are owed to him. [...]
If someone does something for himself, but another understands that it was done to honor him, one does not have to correct this misunderstanding.
But
Exceptions to the Exceptions
Despite these allowances, one should always attempt not to say an outright lie, but rather to tell half truths.
Even in these cases, one should try to avoid lying to children, so as not to train them to lie.
Also, even in these circumstances, one should try not to lie on a constant basis.
The Magen Avraham says that even in the above circumstances, one may only lie about the past but not about the future. For example, one may not say: "I will do such and such" in order to make peace. Others question this ruling.
These sources make no distinction between the jew and the non-jew, or the age of the recipients. One should simple not lie, regardless of whether they are jewish or not. It is expressely forbidden to lie to non-jews and jews alike under the concept of Geneivat da'ath (גניבת דעת) Chullin 94a
As Shmuel said: It is forbidden to deceive anyone, even an idolatrous gentile
If it is necessary to lie for the sake of peace (such as taking the blame for one's parent when confronted by the other parent) one may do so, although it is preferable to still stay as close to truth as possible.
