"Making half swings teaches good arm extension."
If you want to boost the quality of your iron play, practice hitting half shots with a 9-iron. Swing back to where your left arm is parallel to the ground, then swing through to where your right arm is parallel to the ground. Your goal is to keep your left arm extended as you go back and both arms extended as you swing through—even well past impact (above).
Keeping the arms stretched on both sides like this helps improve three critical facets of iron play: (1) FACE CONTROL: It reduces the need to make any adjustments with your hands to square the face. (2) SWING PATH: The club will travel more on the ideal in-to-out path in relation to the target line. (3) COMPRESSION: The club will move on a downward angle even past impact, which promotes solid contact.
Note: The divot I took here was in front of the ball's position at address. I hit down on it, and the ball jumped off the face.
Should you be using a 4-iron instead of a hybrid? The answer is no, unless you can swing a long iron approaching the speeds we see on tour. For most players, the design of a hybrid makes it so much easier to hit a long, high shot with adequate spin, which is exactly why there are so many LPGA Tour players using them. If they're good enough for the pros, they're good enough for you.
Sean Foley is a Golf Digest Teaching Professional.