What are the four major tournaments for the Professional Golfers Association?

The four major tournaments for the Professional Golfers' Association (PGA) Tour are the Masters, the PGA Championship, the US Open, and the British Open.  The Masters is the first tournament of the calendar year and is held in April in Augusta, Georgia, USA.  The PGA Championship comes second and is held in May followed by the US Open in June and the British Open in July.  The PGA Championship, US Open, and British Open are held at different venues each year whereas the Masters tournament is always held at Augusta National Golf Club.  The Masters, US Open, and British Open all welcome qualifying amateurs and professionals alike whereas the PGA Championship is limited to professionals only.