© 2005, Chicago Tribune Company.

April 23, 2005

From the time his daughter was about 5, University of Chicago mathematician
Saunders Mac Lane used to take her for walks in the city or hikes in the woods,
pointing out landmarks along the way.
April 23, 2005

** SAUNDERS MAC LANE, 95
University of Chicago mathematician helped introduce key concepts to field **

Russell Working, Tribune staff reporter.

As they returned, he would ask her to guide them back, Gretchen MacLane recalled. He wanted her and her sister to know how to find their way through memory and logic.

Dr. Mac Lane, 95, called one of the most influential 20th Century American mathematicians, died of constrictive heart disease Thursday, April 14, in a hospice near San Francisco.

A formal man who wore a hat and tie even while relaxing at home, he made a lasting impact on his field during his career, which extended into his 90s. In 1945, Dr. Mac Lane co-wrote a paper that introduced concepts such as "category theory," which deals in an abstract way with mathematical structures and relationships between them.

"There are some ideas you simply could not think without a vocabulary to think them," said J. Peter May, a professor of mathematics at U. of C. "And the language that they introduced made huge swaths of modern mathematics possible."

Dr. Mac Lane was born in Norwich, Conn. His father, a Congregationalist pastor, died when the future mathematician was 13. His mother taught math, Latin and Greek in prep schools to support the family, said Gretchen MacLane, who later dropped the space in her last name.

He received his bachelor's degree at Yale University in New Haven, Conn., and his master's at the University of Chicago in 1931. He went on to study at the University of Goettingen in Germany, then the world's leading center for mathematics, May said. But storm clouds began gathering after Adolf Hitler became chancellor in 1933.

"When he first went there, it was glorious," his daughter said, "but then as it went on, more and more Jewish professors were removed from their posts, and most of the mathematicians were Jewish."

Dr. Mac Lane met his first wife, Dorothy Jones Mac Lane, at the U. of C., and they married in 1933 in Goettingen, where she had come to type his doctoral dissertation, his daughter said. She died in 1985. Dr. Mac Lane later married his second wife, Osa Segal Mac Lane.

Dr. Mac Lane taught math at Harvard, Cornell and the University of Chicago before getting a permanent position at the U. of C. in 1947. He became a professor emeritus at the U. of C. in 1982 but continued to teach and advise students.

Dr. Mac Lane was active in scientific and math organizations, and he won the National Medal of Science.

His work in many areas, such as algebraic field theory, has "the character of continuing influence and daily applicability," said F. William Lawvere, professor emeritus of math at the State University of New York in Buffalo. "His powerful teaching left a lasting impression that still reverberates."

Dr. Mac Lane's formal demeanor led his daughter to begin calling him by his first name after she reached adulthood "He seemed too dignified for `Daddy,'" she said.

But he loved skiing and hiking, and he would read aloud the works of poets, including Byron, Shelley, Keats and Wordsworth, Osa Mac Lane said.

"And so I was reading poetry to him -- those same poets -- when he was lying there at the end of his life," Osa Mac Lane said.

Survivors also include another daughter, Cynthia Hay; three stepchildren, William Segal, Andrew Segal and Karen Segal; a grandson; and five stepgrandchildren.

Funeral services were held in San Francisco.

I'm fond of Mac Lane because he loved telling stories and reciting poems. He enjoyed being the center of attention at his 90th birthdary party at a category theory conference in Coimbra, Portugal, where I gave a course on n-categories. Later, when I visited Chicago, he told me I had to write a book explaining this stuff. I will!

Take a look at Mac Lane's mathematical biography and a retrospective at the University of Chicago.

© 2005 John Baez

baez@math.removethis.ucr.andthis.edu