definition by example

Tonight in class, our professor was talking about correlations between matched/paired vs. non-matched/non-paired and he chose not to give a definition as to what those are. I won't speculate on the reasoning behind his choice; I'll just say he chose to define them by giving examples.

I only bring this up because I did the same thing today in class and therein lies my question. Is this a valid way to teach students the definition of a term/word? Because I can tell you I didn't really get a good grasp on the meaning of these two contrasting educational research terms.

I wonder if my students felt the same way about the terms I was working with in class this morning? We were talking about constructive and destructive interference. I defined those two terms for them, but I chose not to define in-phase and out-of-phase. This refers to two signals which either correspond directly (in-phase) or are offset from each other (out-of-phase). Signals can be anywhere from zero to 359 degrees out of phase with one another. I guess my one saving grace is that I did a demo using two phase-shifted speakers which completely cancel the sound from the other speaker. Its my favorite demo of the year, by the way.

I will be revisiting phase shift with students tomorrow. Even if there is a chance students feel half as vague about phase as I do about about matched pairs, I need to re-teach the concept. At the bare minimum, I'll be asking if anyone has any questions at all about phase and I will certainly think twice before teaching "definition by example" next time.