Institutio Oratoria

For if to slay a man is often a virtue and to put one's own children to death is at times the noblest of deeds, and if it is permissible in the public interest to do deeds yet more horrible to relate than these, we should assuredly take into consideration not solely and simply what is the nature of the case which the good man undertakes to defend, but what is his reason and what his purpose in so doing.

And first of all everyone must allow, what even the sternest of the Stoics admit, that the good man will sometimes tell a lie, and further that he will sometimes do so for comparatively trivial reasons; for example we tell countless lies to sick children for their good and make many promises to them which we do not intend to perform.