Cannot set reminders with Siri. Siri says I need to d/l an app first

Whenever I try to set a reminder with Siri, I get the following response: "I don't see an app for that. You'll need to download one." I'm fairly certain that it's due to some setting that I changed myself without realizing the repercussions. I'm pretty sure that I used this feature at least once when I got my iPhone just a few months ago. I only noticed that I was not able to set reminders with Siri when I tried to set one today and got the above error message... Can someone please help me figure this out? Thanks in advance!