This has been a remarkably easy time to be a bull.
September is set to be the 11th straight month in which the has either risen, or has fallen by less than 0.1 percent. If stocks continue to act well in the second half of the month, that will make this the longest such streak for stocks in 58 years.
Going back to 1928, the S&P has only seen four prior streaks in which the index avoided posting a monthly drop of more than 0.1 percent in 11 or more straight months, according to a CNBC analysis of FactSet data. The most recent run was the longest ever, stretching from March 1958 to May 1959, before being broken with a 0.4 percent June decline.
Prior streaks went from 1953 to 1954, from 1949 to 1950, and from 1935 to 1936.
In a sense, the recent streak is emblematic of a markedly restrained level of stock market volatility. While it hasn't seen a monthly loss of more than 0.04 percent, the S&P 500 hasn't seen a monthly gain of more than 3.7 percent in the past year, either. Contrast that to the 1958 to 1959 period, when the S&P rose more than 4 percent in three separate months.
Interestingly, 1959 is notable to stock market historians as the year in which bond yields surprised many by breaking decisively above stock dividend yields. Richard Sylla, the Henry Kaufman professor of the history of financial institutions and markets at NYU's Stern School of Business, has pinned that shift on increasing public trust of corporate reporting, which spurred greater optimism about equities.
When asked about the recent streak, Boris Schlossberg of BK Asset Management commented Wednesday on CNBC's "Trading Nation " that "it's definitely historically interesting" — but added that he certainly wouldn't make any investment decisions based on it.
"The stock market trades on forward guidance, and every day is independent of the day beforehand, so we really can't make any kind of investment conclusions from the fact that we've had very strong uptrends so far," Schlossberg said.