In the late 1720s the Caribbean pirates' flourishing community was brought to a screeching halt. An enhanced British naval presence was partly responsible for this. But, as I discuss in The Invisible Hook, most important in bringing pirates to their end was a series of early 18th-century legal changes that made it possible to effectively prosecute pirates.

In the years before 1536 England tried pirates in its Admiralty courts under the civil law. Convicting an accused pirate proved very difficult, however. Civil law rules required an accused pirate to confess his guilt or two eyewitness, neither of whom could be accomplices, to testify to his piracy. Such eyewitnesses were hard to come by, and pirate confessions, even harder. Thus many pirates escaped conviction.

To rectify this problem, in 1536 England introduced the Offenses at Sea Act, which kept piracy a crime at civil law but allowed pirates to be tried via common law rules. Under this procedure the fate of accused pirates was decided by a jury of 12 men and, crucially, accomplice testimony was permitted.

The Offenses at Sea Act was helpful but eventually proved insufficient. In the 17th century, pirates were increasingly active in and around England's distant and growing colonies. Under the 1536 law, accused pirates and potential witnesses had to be shipped to England for trial at the capturing colonial government's expense. Rather than bear this cost, many colonial governments simply let pirates go instead.

Out of this unfolding of events emerged the Act for the More Effectual Suppression of Piracy, initially introduced by parliament in 1700. This act permitted colonial governments to try and execute pirates on location. (It also eliminated jury trials for pirates, placing their fate in the hands of colonial-appointed commissioners, but continued to permit accomplice testimony). No longer constrained by the need to send pirates to England for trial, the 1700 law proved to be a critically important legal change for bringing pirates to justice.

The initial act was set to expire seven years after its introduction but was made permanent in 1719 when the pirate population began exploding and when various additions to the act, such as rewards for capturing pirates, and punishments for pirate consorters, were also introduced. In 1721 further modifications were made, including a provision for punishing armed merchantmen that refused to fight their pirate attackers.

The effect of these early 18th-century legal changes was to significantly increase the risk, and thus the cost, of pirating after 1719 and 1721 in particular. Whereas only 31% of all pirates hanged between 1704 and 1726 (for which I have data readily available) were hanged in the 15 years spanning 1704-1718, 69% were hanged in the mere seven years spanning 1719-1726 (with the vast majority of these occurring in the years spanning 1721-1726). This posed a significant problem for pirates because as the legal cost of piracy rose, pirates' ability to find willing recruits declined, threatening the viability of their criminal enterprise.

But pirates did not sit on their laurels in the face of tightening legal screws. Although they ultimately failed in their efforts, for a short time, at least, they succeeded in partially offsetting the rising legal costs of piracy, helping them to continue to find the recruits they sought. Pirates achieved this by exploiting a loophole in anti-piracy law that let off any man who could demonstrate to the court that he was a "forced man," pressed against his will into pirates' service. The "forced" defense was plausible since pirates sometimes did conscript sailors (though it seems that in general this was not the case, volunteers from overtaken ships sometimes being more numerous than the overtaking pirate crew was willing to have). Pirates exploited this loophole in several ways. But perhaps the most interesting was their reliance on "ads of force," which proved to be a remarkable recruiting tool for pirates.

An ad of force was a newspaper ad, published by an allegedly conscripted sailor's released captain or fellow seamen on behalf of their forced compatriot, publicly certifying that the sailor had been "forced against his will" to join so-and-so's pirate crew on this such-and-such date, etc. If this pirate crew was ever captured--an increasingly likely event after 1719 and 1721 owing to the legal changes discussed above--the ostensibly forced sailor could point to his ad in his defense at his trial and the court might consider this evidence for his claim, thus increasing his chances of being let off.

Ads of force were an excellent invention for conscripted sailors. But they were equally excellent for volunteers who wanted a little insurance against the greater risk of their newly chosen trade. An ad of force was far from an iron clad means of getting off at a pirate trial. But it certainly helped. (It was most helpful when used in conjunction with other evidence of alleged innocence, which pirates also concocted, but which there's not space to discuss here). Courts considered it and some sailors appear to have been acquitted at least partially on the basis of such ads--some no doubt legitimately, but for many others this was simply their pirate insurance policy paying off. Pirates thus managed to use ads of force to help offset the rising cost of piracy in the early 18th century and in some cases were eager to remind merchant sailors they sought to recruit that they could use this device to help persuade them to join.

Notably, the popularity of ads of force tracks the risk of pirating, which in turn tracks changes in anti-piracy law during this period, quite well. Of all those ads of force published in the Boston News-Letter between 1704 and 1726, for instance, only 7% appear in the 15 years spanning 1704-1718, while 93% appear in the mere seven years spanning 1719-1726, the bulk of these again appearing between 1721 and 1726.

As discussions begin moving forward about how legal changes might be used to help suppress modern pirates, it's useful to look to the past to see what problems were confronted in prosecuting pirates historically, what was useful for overcoming these problems, and what wasn't. Similarly, as modern pirates, eager to persuade courts of their innocence, begin to come under the purview of various nations' legal systems, it's useful to recall that pirates, like other people, are unlikely to be passive responders to the law. Rather, as (or if) the law becomes an important constraint on their behavior, pirates may seek to offset the law's effects in unanticipated ways, manipulating the law as the law seeks to manipulate them.

As this is my final day guest-blogging for the week, I'd like to thank Eugene for kindly inviting me to do so and those of you who offered thoughtful comments for participating in the discussion. I greatly enjoyed the opportunity and conversation.