Canon Drive Modes

I was asked yesterday, and I couldn’t clearly remember what the exact difference between each mode is. So I looked it up and decided to add a post this morning before I forget.
Canon cameras have three auto focus modes.
One-Shot, AI focus and AI servo.

One-Shot This mode is best for still subjects, when you hold down the shutter button halfway the camera will focus then lock on focus point. As long as you are holding the shutter halfway focus will stay locked on that point.
See my post on back button focus for easier way.

AI Servo
This one is used for moving subjects when the focusing distance changes. The camera will focus continuously as long as you are holding the button.

AI Focus
This uses both the above modes. It will switch automatically from One-Shot to Servo if the subject starts moving.

It really is quite simple, but for some reason I just couldn’t provide a 100% confident answer yesterday.