“We must believe in free will — we have no choice.”
An ironic statement which Singer made in many interviews over many years; here quoted in "Isaac Singer’s Promised City" http://www.city-journal.org/html/7_3_urbanities-isaac.html City Journal (Summer 1997)
Variants or variant translations:
We must believe in free will — we have no other choice.
You must believe in free will; there is no choice.
We have to believe in free will. We’ve got no choice.
This makes more sense if you consider the statement "we must believe in free will; we have no [other logical] choice"
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Isaac Bashevis Singer 39
Polish-born Jewish-American author 1902–1991Related quotes

New Year Message as Conservative candidate for Dartford (29 December 1950) http://www.margaretthatcher.org/document/100896
1950s

Lee Kuan Yew, Legislative Assembly Debates, April 27, 1955
1950s

1960s, Inaugural address (1965)
Context: In each generation, with toil and tears, we have had to earn our heritage again. If we fail now, we shall have forgotten in abundance what we learned in hardship: that democracy rests on faith, that freedom asks more than it gives, and that the judgment of God is harshest on those who are most favored. If we succeed, it will not be because of what we have, but it will be because of what we are; not because of what we own, but, rather because of what we believe. For we are a nation of believers. Underneath the clamor of building and the rush of our day's pursuits, we are believers in justice and liberty and union, and in our own Union. We believe that every man must someday be free. And we believe in ourselves.

“We must never forget that it is through our actions, words, and thoughts that we have a choice.”

The Magnificent Defeat (1966)

As quoted by Raymond Lonergan in Mr. Justice Brandeis, Great American (1941), p. 42.
Extra-judicial writings