These are not interchangeable, yet I see the confusion all the time. So, I thought I’d drag out a retread to remind everyone to pay close attention to when they use “Who” and when they use “That.”
Thar be a difference, and it’s that wee difference that keeps bleary-eyed editors from downing an entire pitcher of the beagle’s margaritas.
What she said. Plus: it’s/its (especially this), there/their/they’re, and who/whom.
Lest you think I’m perfect (though you probably should) I’ll confess to still having trouble with “that/which.” Yes, I know the difference; I just can’t be sure any time I use it. Dang brain. Hey, Lynn, pass that pitcher over here, will ya?