Two phrases have been bumping together in my head the last day or two: "extenuating circumstances" and "mixed motives." I'm not exactly sure what got these particular phrases rumbling in my mind: a conversation with my daughter, the first episode of "The Jewel in the Crown," the protests at the South African Embassy and a segment on South Africa on Sunday night's "60 Minutes"; perhaps other things as well. In fact, certainly other things as well: the extenuating circumstances I frequently find to explain -- to myself, at least -- why I have not done those things which my conscience tells me I ought to have done, and, of course, to excuse myself for not having done them; and the mixed motives I bring to almost any undertaking.

There are, of course, always extenuating circumstances; and all motives are mixed. Yes, and things are more complicated than they seem, too. To say these things is not to say much, except to encourage us in our natural passivity and sloth -- perhaps I should speak only for myself -- and in my own particular reluctance to change that familiar and often comfortable enough condition. The familiar has the virtue of being known, at least, and change can be and often is quite terrifying, even violent, until the new settles in and becomes familiar in its turn. At best it is unsettling and disturbing. As Antonio Gramsci, the Italian Marxist, wrote in his "Prison Notebooks": "The crisis consists precisely in the fact that the old is dying and the new cannot be born: in this interregnum a great variety of morbid symptoms appears."

But the new, of course, will be born. I thought of Gandhi -- reminded by "The Jewel in the Crown" -- and his unreasonable and stubborn campaign, in the dark days of World War II, to force the British to quit India. I thought of the apparent reasonableness of South African President P.W. Botha's words on "60 Minutes" Sunday night, and of the rather cheerful depiction of that benighted country in the current film "The Gods Must Be Crazy." I thought of our own government's sanguine and reasonable policy of "quiet diplomacy" and "constructive engagement" to affect "evolutionary" change there. And I thought of Bishop Desmond Tutu, who last week was in Oslo to accept the Nobel Peace Prize, standing in June 1982 in clerical robes outside a cathedral in the black township of Soweto, raising a cross in his hands until a white policeman stopped beating an elderly black man. Bishop Tutu, as committed to nonviolence as Gandhi and as intense in his moral passion, called our official policy toward South Africa "evil, immoral and unchristian."

The situation in South Africa is "complicated," of course, and there are many "extenuating circumstances," as there were in India during World War II, as there are in every place and time; and all motives are mixed. I don't suppose Sen. Kennedy and the Rev. Jackson are unaware of the political value at home of their projected visits to South Africa next month, but what may be politically expedient is not for that reason wrong. What is wrong is that the 73 percent black majority in South Africa have the most minimal control over their lives, that they cannot freely move from place to place without permission though they can be moved without consent, and that they live in the last country on earth where the domination of one race -- their own -- by another is perpetuated by law, where one race -- the white race -- wants to keep what it has and where the blacks have virtually nothing to lose.

There is nothing complicated about that. Some things are simply wrong. We know it in our hearts, no matter how many "extenuating circumstances" or "mixed motives" or other complicating factors our clever minds may come up with. That is why we need heroes and saints -- like Bishop Tutu, like Gandhi: to remind us of how simple some things really are.