difficult as the USGA does. The PGA of America enters into a profit-sharing agreement with the host club. (An exception was in 2014, when the tournament was held at Valhalla Golf Club in Louisville, Kentucky, a club that the PGA of America fully owned at the time.) As with The Masters, previous winners of the PGA Championship have a lifetime invitation to compete. As well as inviting recent champions of the other three professional majors and leading players from the world rankings, the PGA Championship field is completed by qualifiers held among members of the PGA of America, the organization of club and teaching professionals that are separate from the members of the PGA Tour. The PGA Championship is also the only one of the four majors to invite all winners of PGA Tour events in the year preceding the tournament, as well as inviting 20 club professionals who are non-tour regulars. Amateur golfers do not normally play on the PGA Tour, and could only qualify by winning one of the other three majors, winning a PGA Tour event while playing under a sponsor's exemption, or having a high world ranking. When the PGA Championship was held in August, it was frequently affected by the high heat and humidity that characterize the summer climate of much of the U.S., which often set it apart as a challenge from (in particular) the Open Championship, an event often played in cooler and rainy weather. With the 2019 move to a May date, heat and humidity are less likely to have major effects on the competition. The third major, the U.S. Open, is notorious for being played on difficult courses that have tight fairways, challenging greens, demanding pin positions and thick and high rough, placing a great premium on accuracy, especially with driving and approach play. Additionally, while most regular tour events are played on courses with par 72, the U.S. Open has almost never been held on a par-72 course in recent decades; the 2017 event was the first since 1992 to be played at par 72. During this time, the tournament course has occasionally been played to a par of 71 but most commonly par 70. The U.S. Open is rarely won with a score much under par. The event is the championship of the United States Golf Association, and in having a very strict exempt qualifiers list – made up