In an era of dominant pitching, Clayton Kershaw has clearly established himself as the game's most dominant pitcher. With only a few starts remaining, the Dodgers' ace has become the leading candidate for the National League MVP award, an honor no NL pitcher has won since Bob Gibson in 1968.

But how great is Kershaw's season? One way to find out is to rank the top 20 pitcher seasons of the past 50 years.

Ranking the best seasons isn't as easy as looking at Wins Above Replacement. Although WAR adjusts for era and ballpark, which WAR do you use? For example, Baseball-Reference.com, which focuses more on runs allowed, ranks Dwight Gooden's 1985 season tied for first overall since 1965 at 12.1 WAR, but FanGraphs, which emphasizes strikeouts, walks and home runs, ranks it 33rd at 8.7 WAR.

Instead of picking one over the other, I used the average WAR between Baseball-Reference and FanGraphs. Also helpful was a series of articles Bill James wrote earlier this year; he devised a way to evaluate pitchers on a start-by-start basis, factoring in things like park, opponent and era, and graded each start on a scale of 1 to 10.

While durability was important in my evaluation, dominance was a necessity. I also studied the peripherals and tried to balance the different eras of the past 50 years. Finally, postseason performance was also considered; after all, a season doesn't end after game No. 162.

For each pitcher, a quote from that season is included (unless otherwise cited), along with my own commentary.

Note: K% = K/9 rate compared to the league average; ERA+ = ERA adjusted for home park and league context.

Honorable mentions: Juan Marichal, 1965; Denny McLain, 1968; Bob Gibson, 1969; Wilbur Wood, 1971; Bert Blyleven, 1973; Tom Seaver, 1973; Roger Clemens, 1986; Orel Hershiser, 1988; Bret Saberhagen, 1989; Greg Maddux, 1992; Pedro Martinez, 1997; Randy Johnson, 1997; Kevin Brown, 1998; Curt Schilling, 2001; Randy Johnson, 2002; Johan Santana, 2004; Zack Greinke, 2009; Roy Halladay, 2011; Justin Verlander, 2011.