Great pitchers aren't defined as such because they dominate in April.
And great pitching seasons aren't defined as such by one or two quality months out of the entire campaign.
The defining characteristic of a great pitching season, historically, is its finish. Not surprisingly, the final two months are also the toughest and most taxing part of the season for the pitcher.
As the Dog Days roll in, the job of a big league starter doesn't get any easier. Fatigue begins to set in, pressure mounts and innings totals rise.
Yet there are some pitchers who seem to thrive when the season would seem to pose its toughest test.
Clayton Kershaw, the Dodgers' ace who currently leads the National League in ERA, WHIP (walks plus hits per inning pitched) and hits per nine innings, is a prime example. Despite his remarkable stats thus far, Kershaw's history indicates that those numbers may get even better.
Since his debut season of 2008, Kershaw's ERA has declined after the All-Star break in every season. His career 2.36 second-half ERA is far and away the best mark among active pitchers with a minimum of 20 starts.
"The fact that he can come out every single start and reproduce what he does is what makes him the best in the league," Kershaw's catcher A.J. Ellis said.
Maintaining that consistency through the season's finish is easier said than done, of course. The majority of top-tier starting pitchers will see their ERAs begin to rise in the season's second half -- whether due to fatigue, workload or simply the law of averages.
Last season, Chris Sale's ERA rose nearly an entire point from the All-Star break to season's end. He has a chance to change things this year after putting together a similarly impressive first four months.
But a rising ERA is common for young arms still adapting to the length of a big league season. Justin Verlander's ERA rose in the second half in each of his first four seasons in the Major Leagues. Now, he's considered one of baseball's best finishing arms.
After Kershaw, only three other players on active rosters sport career second-half ERAs below three -- Madison Bumgarner (2.84), Adam Wainwright (2.92) and Jeremy Hellickson (2.93).
It's by no means easy to improve once the season wears on. But history tells us the great ones find a way to do it.
Want some help foreshadowing this season's Cy Young Award winners? Well, they had better be traditionally solid finishers.
In the past 10 seasons, 16 of the 20 Cy Young Awards have gone to pitchers whose career second-half ERA is lower than their first-half ERA. Only Verlander, R.A. Dickey, Cliff Lee and Brandon Webb don't fall within that group.
The Yankees' CC Sabathia is one of the league's best-known finishers. He turned on the jets in his Cy Young Award-winning 2007 campaign, posting a 2.57 August ERA and a 2.37 mark in September/October. Perhaps more famously, a year later, after being traded to Milwaukee in early July, Sabathia posted a 1.65 ERA and led the Brewers to their first playoff appearance in 26 years.
The left-hander has struggled mightily this season, but the numbers indicate there is no time more ripe for a turnaround than the Dog Days.
"I feel like it has to turn, it's going to turn, but it's just not at that point yet," Sabathia said recently.
Fittingly, many of this year's early Cy Young Award candidates have already had past success closing out seasons strong.
In the American League, Felix Hernandez boasts a 3.10 second-half ERA, and his August ERA over the past five seasons is tops in the AL. Max Scherzer has posted a 2.98 ERA over the past three Septembers combined. Hiroki Kuroda, meanwhile, has posted an ERA of exactly three in the season's final two months and a record of 25-15. (Not bad, compared with his lifetime 42-48 record and 3.41 ERA in the first four months.)
Kershaw leads the charge in the National League and his second-half success has been well documented. But, statistically, Wainwright and Bumgarner -- each of whom has already put together a solid season -- are second and third among active pitchers in second-half ERA.
All of the aforementioned hurlers have put together four brilliant months. But the history books aren't written based on parts of seasons.
For these pitchers to etch their mark, they'll have to finish as strong as they started, a task that has traditionally separated the good pitchers from the great ones.
AJ Cassavell is a reporter for MLB.com. Follow him on Twitter @ajcassavell.