Armstrong on the moon. (Photo: NASA)

When Neil Armstrong walked on the moon in 1969, he uttered a series of words. “One small step”…but for whom? Most famously, the quote is “One small step for man, one giant leap for mankind.” But Armstrong has said that version is missing one tiny detail. The real quote, according to Armstrong, should be: “One small step for a man.”

For years, linguists have tried to suss out the definitive answer to this mystery. In a new paper, published in PLOS ONE, a team from University of Oregon, Michigan State and Ohio State lay out more evidence that it’s at least possible that Armstrong said “for a man,” just like he maintained.

The difference here is so small—“for a” vs. “for”—that it’s extremely hard to distinguish one possibility from the other. Examinations of the audio of the quote did not resolve the question. In the new study, the linguists don’t look directly at the quote, but instead consider its context—the production of these words and our perception of them. In other words, how do people in the area of Ohio where Armstrong grew up say “for”? How do they say “for a”? And could the way in which he spoke the whole sentence affect how we perceive it?

The bit of speech at issue here is very short, just 127 ms long. In one experiment, the linguists considered what that length might mean. They looked at 191 examples of people from the same area of Ohio saying “for” and 191 examples those same people saying “for a” and measured the length of those words. They found that the people took about the same amount of time to say “for” and “for a.” The average length of “for” was 168 ms; the average length of “for a” was 225 ms.

What that means is that Armstrong could have been saying either “for” or “for a”—either still makes sense. But while Armstrong’s bit of speech is “highly compatible” with either possibility, the linguists write, and while there’s no statistical significance between the two groups, the 127 ms duration is “slightly more compatible” with the possibility that he said “for man.”

In the second experiment, though, the linguists looked at how Armstrong’s rate of speech might have affected how others heard what he said. He was speaking quite slowly, and, in context, said “for” or “for a” relatively quickly.

Although it’s counterintuitive, his slow rate of speech might have made it more likely that people misunderstood him. Human brains do some very impressive analysis to clip words out from the babble of sound we use to communicate, and they depend on contextual clues. Slower speech indicates to the brain that there are probably fewer words involved, and since Armstrong was speaking slowly, that could bias our brains towards hearing “for” instead of “for a.”

In this experiment, the linguists played clips of people using “for a” in sentences where “for” would have worked just as well. (“Y’know I was there just for a half a day,” for example.) Sometimes they played the clips at a normal rate and sometimes they slowed down the rate of speech around the “for a.” When the clips were slower, the listeners were more likely to miss the “a” and hear only “for.”

These studies show two things. First, Armstrong could have said “for a.” He took more than enough time to squeeze in both words. Second, because he was speaking slowly, we could have heard him incorrectly—the slow pace of his speech actually made it more likely others would mishear him.

This doesn’t solve the mystery of the missing “a” one way or another. But it keeps open the possibility that Armstrong really did add in that little article. “One small step for a man, one giant leap for mankind.”