All truths are half-truths.
Verified
insighttruthSource: Dialogues of Alfred North Whitehead, as recorded by Lucien Price, 1954
Genuine Whitehead, recorded by Lucien Price. The full remark is 'There are no whole truths; all truths are half-truths. It is trying to treat them as whole truths that plays the devil.' The corpus quotes only the middle clause, which is the form that circulates. Source is a recorded conversation rather than Whitehead's own pen, but Price's Dialogues is an accepted and dated primary record.