Arlene Alda, 81, and her husband, the actor Alan Alda, 79, say that one secret to a long-lasting marriage (theirs has been going for almost 58 years) is forgetfulness, which comes naturally to them at this point.

The Aldas, who discussed their decades together by telephone, with Ms. Alda also weighing in later by email, haven’t had a serious argument for the last 20 years, she said, primarily because they can no longer remember for very long whether they are angry with each other or why.

“I have a short memory, and so does he,” Ms. Alda said. “Was that always true? I don’t recall.”

Both emanate warmth and thoughtfulness in the way of beloved English professors or concerned therapists. Mr. Alda, whose career in television and theater has been as remarkably durable as his marriage, and Ms. Alda, a writer and photographer, possess laughs that are like old jeans: comfortable and well used.

Ms. Alda said that laughter is “the real glue that keeps us happily and willingly stuck together.” They are definitely not the kind of couple who sit silently across the table from each other. “We’re both loud laughers,” she said. “Guffawing ones.”