I suppose so
I reluctantly agree, I guess so, as in Do you want tickets to the concert?—I suppose so, or Do you think it's going to rain?—I suppose so. [Mid-1500s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.