I used to be one of the "Never, ever step backwards except down the line of dance" people, mainly because I was tired of newbies and oldies drilled in the "Dreaded 8-count Basic" School of Argentine Tango whacking me or my partner with their unconscious back-step against the line of dance on count 1.
But after having my instep drilled a couple of years ago by someone taking a backstep perpendicular to the line of dance from an adjacent lane, I realized the problem was not the backstep itself. I recalled a class I took with Seattle tango guru Evan Wallace one cold December evening when we all huddled around the fireplace at the Wilsonian to stay warm. Evan had us dance in the small area in front of the fireplace, and that was the first time I ever heard of Evan's Rule.
So here is the reprint of his original TANGO-L posting (Apr 19 2001), courtesy of the redoubtable Mr. Wallace:
The backstep is not the culprit here. It is merely the most common step used to violate one of the most important principles of social dancing. That principle is: "Never move into a space unless you can verify with complete certainty that
it will be vacant when you arrive."
This principle sounds simple, but requires a few clarifications:
"Never" means never. Ever. I mean it.
"Vacant" means vacant at the time you will occupy the space, not at some time in the recent past (e.g., the last time you looked). To know that a space will be vacant a moment hence, you need to know with complete certainty that there are no other couples on the floor that could come to occupy that space on or about the same time you will arrive there (in the vernacular, a "crash").
"Verify with complete certainty" means, well, verify with complete certainty. This involves the senses, chiefly sight and sometimes hearing (if taste is involved, something has gone badly wrong), along with other mental faculties. One way to verify with complete certainty that a space will be open when you arrive there was alluded to above: a) visually verify that a space on the floor is open; b) locate all couples who are within "striking distance"; and c) mentally deduce, based on their current positions and velocities, whether any of these couples could conceivably reach this same spot in roughly the same amount of time as it takes you to get there. If this cannot be verified with complete certainty, do not take the step. (See "Never" above).
In some cases, one does not have to visually verify that a space is free before moving there. For example, if the leader does a check step forward (along the line of dance, say), and moves immediately back into the space he just occupied, he knows the space is free by virtue of the fact that he was just occupying it a moment earlier--as long as he had already verified, with complete certainty, that no other couple could get close to this spot in the amount of time that it took to perform the check step.
Evan Wallace
Seattle, Washington
Sadly enough, most people dance as if they were the only ones on the floor.
----Michael