One of my most embarrassing moments in my life concerns a time I was teaching a trick based on the Gilbreath Principles.

On one of my very first visits to Gary Darwin's Midnight Magic Club in Las Vegas, I joined a group of people who were performing and teaching tricks to each other, with each person taking a turn. When it got to be my turn, I performed and taught Terry LaGerould's Best Bet Yet from his book, A Magical Baker's Dozen. When it came time to teach it, I also tried to make sure everyone at the table understood the Gilbreath Principle behind it, as well. I finished, and stayed until others had taken their turn.

Later that same night, I had the honor of talking to Gary Darwin. I introduced myself, and mentioned my interests in mathematical effects. When Gary heard this, he asked one of the attendees to come over. I recognized this man as one of the people from the table where I had been earlier. Gary Darwin says to me, "You should get to know this gentleman, as he also likes mathematical card effects. Scott, meet Norman Gilbreath!"

Yep, I had actually spent part of one night teaching the Gilbreath Principle to Norman Gilbreath. I apologized for not recognizing him and knowing who he was, and he was very gracious. He replied, "That's OK. By the way, you taught the principle very well."

Moving on from my embarrassment, I'd like to work on just that - teaching the Gilbreath principle. When seen in action, the effects can be mind boggling, so it seems like it would be difficult to understand. Fortunately, Bitwise Magazine spends time not only explaining the Gilbreath Principle, but doing so in an extremely clear and understandable manner. In Martin Gardner's book, Aha! Insight/Gotcha, he teaches a simple trick that helps make clear the power of Gilbreath Principle when presented to an audience.

You'll often hear references to the First and Second Gilbreath Principles. The second, as it turned out, is actually a generalization of the first. To understand each of these versions, and the differences, Card Colm makes the differences clear in two magic effects, The First Norman Invasion and The Second Norman Invasion.

Colm Mulcahy has also written up a Gilbreath-based effect called An ESPeriment with Cards (PDF), applying the principle to Zener Cards.

These are some excellent resources for starting to explore this fascinating principle. This is one of those principles that, even when you know you're using it, it will still amaze you!