There are specialists in these matters!
"In actual fact, the Jesuit casuists deal with two forms of permissible deception, that of 'amphibology' and that of reservatio mentalis. 'Amphibology' is nothing else than the employment of ambiguous terms calculated to mislead the questioner; 'mental reservation' consists in answering a question, not with a direct lie, but in such a way that the truth is partly suppressed, certain words being formulated mentally but not expressed orally.
"The Jesuits hold that neither intentional ambiguity nor the fact of making a mental reservation can be regarded as lying, since, in both cases, all that happens is that one's neighbor is not actually deceived, but rather his deception is permitted only for a justifiable cause.'''–'' The Power and Secret of the Jesuits," pp. 154, 155.
The Jesuit Gury gives examples of this; among others he says:
"Amand promised, under oath, to Marinus, that he would never reveal a theft committed by the latter .... But . . . Amand was called as a witness before the judge, and revealed the secret, after interrogation.
"He ought not to have revealed the theft, . . . but he ought to have answered: 'I do not know anything,' understanding, 'nothing that I am obligated to reveal,' by using a mental restriction .... So Amand has committed a grave sin against religion and justice, by revealing publicly, before the court, a confided secret."–"The Doctrine of the Jesuits," translated by Paul Bert, Member of the Chamber of Deputies, Professor at the Faculty of Sciences (in Paris), pp. 168, 169, American edition. Boston:1880.
Alphonsus de Liguori, the sainted Catholic doctor, says in "Tractatus de Secundo Decalogi Praecepto," on the second [third] precept of the decalogue:
"One who is asked concerning something which it is expedient to conceal, can say, 'I say not,' that is, 'I say the word "not" since the word 'I say' has a double sense; for it signifies 'to pronounce' and 'to affirm':now in our sense 'I say' is the same as 'I pronounce.'
"A prisoner, when lawfully questioned, can deny a crime even with an oath (at least without grievous sin), if as the result of his confession he is threatened with punishment of death, or imprisonment, or perpetual exile, or the loss of all his property, or the galleys, and similar punishments, by secretly understanding that he has not committed any crime of such a degree that he is bound to confess.
"It is permissible to swear to anything which is false by adding in an undertone a true condition, if that low utterance can in any way be perceived by the other party, though its sense is not understood."–The Latin text, and an English translation of the above statements are found in "Fifty Years in the Church of Rome," by Father Chiniquy, chap. XIII, and in "Protestant Magazine," April, 1913, p. 163.
http://www.sundaylaw.net/books/other/edwardson/facts/fof27.htm
Topic: Taqiyyah anyone??