SARASOTA, Fla. – The next two days could go a long way in defining the shape of the 2012 Red Sox season-opening rotation.

On Saturday, Alfredo Aceves will get the start for a Red Sox split squad team against the Phillies in Fort Myers, while across the state, Felix Doubront will take the ball in Jupiter against the Marlins. On Sunday, Daniel Bard is slated to start for the Sox in Dunedin against the Blue Jays.

All three pitchers -- who, along with Aaron Cook, represent the four candidates for the final two spots in the rotation -- are slated to pitch as many as six innings at a time when the Sox are nearing the point where they will have to consider giving pitchers distinct roles as starters or relievers.

The Sox have not yet decided who will break camp in their rotation. But because one or two of the candidates will need to prepare for a shift to relief for the start of the regular season, there is a chance that this will be the last start of the spring for one or more of the rotation candidates.

With no final decision having been made, what factors will weigh into the Sox’ decision as to who will be in the season-opening rotation? As is usually the case in these sorts of pivotal decisions, it’s complicated.

The Sox are a team with a mission to win now, and so they can ill afford to endure a struggle out of the gate while committing to the development of inexperienced starters. At the same time, the team also faces a need to maximize its starting depth for the season, as last year showed that the quickest way to torpedo a year is through an inadequate number of contingency plans when injuries and underproduction invariably wreak havoc on a staff.

Finally, the team must consider the long-term, and how decisions made now can impact the club not just for the beginning of the season but also for the second half of the season and even into 2013 and beyond.

Based on conversations with multiple talent evaluators inside and outside the Red Sox organization, here is a look at some of the key questions that will go into the Sox’ decision-making process for the back of the rotation, as well as some discussion of how those questions relate to the four starting candidates.

WHAT DO THE RED SOX NEED FOR 2012?

In general, the Red Sox are looking for a pitching staff that can give it the most competitive 1,450 innings (roughly the American League average last year) over the course of a season. The average AL team received roughly two-thirds of those innings (about 982) from its starters, or a bit more than six innings per game.

HOW IMPORTANT ARE THE NUMBER OF INNINGS VS. THE QUALITY OF INNINGS?

There’s no set formula, but suffice it to say that many teams would trade dominance for volume of innings. Call it the Daisuke Problem: In 2008, Daisuke Matsuzaka was 18-3 with a 2.90 ERA but averaged just 5 2/3 innings per start because of his pitch inefficiency. Jon Lester, meanwhile, went 16-6 with a 3.21 ERA while averaging 6 1/3 innings.

Matsuzaka finished fourth that year in AL Cy Young voting. Lester didn’t receive any votes. Yet in the eyes of the Sox, Lester was vastly more valuable because of his ability to work deep into games and leave less to chance in the hands of the bullpen.

The ability to attack the strike zone and remain pitch efficient is thus significant.

WHAT DOES A PITCHER NEED TO DO TO CONTRIBUTE ENOUGH INNINGS TO AVOID STRAINING THE BULLPEN?

When Jonathan Papelbon made his major league debut as a starter in 2005 and again in the spring of 2007, when the Sox considered moving him to the rotation in spring training, Sox manager Terry Francona arrived at a conclusion.

Papelbon, whose curveball was mediocre to the point of uselessness, would strain the bullpen because opponents would foul off pitch after pitch, driving him from the game around the five-inning mark. As a fastball/splitter pitcher, he was best suited for relief.

Red Sox decision makers are now mindful of that lesson. In order to thrive in the American League East, they believe a pitcher needs an arsenal of at least three quality pitches, with above-average command of at least two of them and at least average command of a third.

This is the area of concern for the Sox to date with Bard. In his last outing, for instance, he threw just one changeup because, he said after the game, he felt that he needed to compete with his best pitches and keep his opponents off the board.

Yet manager Bobby Valentine was chagrined to see that Bard didn’t employ a pitch that could be critical for the pitcher’s success. An effective changeup, thrown for strikes, could throw hitters’ timing to the point of getting them to hit early-count groundballs. Even an ineffective changeup, not thrown for strikes, could serve as enough of a show pitch to disrupt batters’ timing on Bard’s fastball.

Two scouts who saw Bard’s start were struck by the fact that the Blue Jays team he faced had foul ball after foul ball on his fastball, with very few swings and misses. Bard ended up throwing 83 pitches in five innings that game, and one of the evaluators felt that he was destined to creep into the 90-100 pitch range through five innings in the absence of a changeup – precisely the fly in the ointment that had Francona wanting to move Papelbon back to the rotation.

Bard has shown a good changeup at times, both in past seasons and even in his second outing of the spring, when he threw three scoreless (and effortless) innings against the Rays. But it remains to be seen how comfortably he can mix all three pitches in key circumstances, or if he will retreat to being a two-pitch hurler in pivotal game sequences.

If that happens, then even if Bard’s fastball and slider are good enough to escape harm, it will be a labor-intensive undertaking that will shorten his outings and potentially strain the bullpen.

Still, the makings of the pitch are there. The potential for it to be a good offering, and one that can make his fastball better, exist.

“His arm action is outstanding,” said an evaluator. “It’s not so much can he do it or not. Does he understand the value of why you throw it? I think that’s where Bobby and he collided. … The changeup controls bat speed. The key to pitching is controlling hitters’ timing. … That’s what Bobby was trying to say. He just has a weird way of doing it.”

As for Bard’s competitors: Aceves features a wild diversity of offerings that he uses in all parts of the strike zone. His fastball/cutter/curve/changeup combination creates unpredictability.

To a degree, the same is true of Doubront, who has the same four pitches as part of his resume. One scout called his outing against the Yankees this spring -- when Doubront tossed four shutout innings -- “stellar,” suggesting that his stuff would have made him an extremely strong option at the back of the rotation.

Cook is in a category unto himself, since he’s basically just a sinker/cutter pitcher. However, his goal with the sinker is to pitch to contact and let the opponents put the ball in play. The late diving action of his signature pitch is so extreme that he’s made a career of being one of the most efficient starters in the majors despite his narrowly defined repertoire.

“The sinker is a special pitch. There’s no question. He’s got the good one,” said one evaluator. “That pitch just bottoms out. I wouldn’t be all that concerned about his velocity coming back.”

WHAT IS THE TRANSLATION OF STUFF FROM THE BULLPEN TO THE ROTATION?

Both Aceves and Bard have shown dominant pitch arrays out of the bullpen. So far, so good for Aceves in taking his four-pitch mix out of relief and showing the same stuff as a starter.

Again, it remains to be seen whether Bard can do the same as he dials back from a max-effort pitcher (albeit one whose delivery out of the bullpen remained smooth) to one who regulates the intensity of his offerings so that he has the strength and stamina to pitch deep into games.

Thus far this spring, Bard hasn’t been getting his typical volume of swings and misses with his fastball. That’s in part by design -- Bard has noted the importance of letting opponents put his heater in play to get quick groundball outs -- but part of the allure of Bard as a member of the rotation is the possibility of having a pitcher who can strike out opposing hitters.

Right now, that isn’t happening, at least not with the same regularity as was the case for the 26-year-old as a reliever. In 12 2/3 innings, Bard has six strikeouts and 10 walks. In his previous three spring trainings, in 27 combined innings out of the bullpen, he had 33 strikeouts and seven walks. 

This is less of a consideration for Cook and Doubront, given that they are merely trying to continue their careers as starters, rather than pursuing a new direction.

WHO HAS SHOWN THE STUFF TO SUCCEED AT THE HIGHEST LEVEL?

It is natural for there to be questions about Bard’s transition from the bullpen to the rotation, and for there to be elements of the unknown. The same is true of Aceves, whose brief experience as a starter for the Sox last year (4 starts, 1-1 record, 5.14 ERA, 13 strikeouts, 13 walks, 5 1/3 innings per start) was not nearly as impressive as his work out of the bullpen.

That said, both Bard and Aceves showed the ability to dominate at the major league level as recently as last season

That separates the two of them from their other competitors.

Doubront has shown interesting flashes of excellent stuff in the majors, but not on a sustained basis, as he has a 4.84 career ERA in 23 big league games over the last two years. Moreover, he has yet to produce a wire-to-wire season of uninterrupted success in the upper levels of the minors, and he’s never thrown more than 129 innings in a season. Given that he logged fewer than 90 innings last year, the Sox would need to be careful with Doubront’s innings, perhaps capping him around 140-160 innings in 2012.

Cook, meanwhile, has shown signs of featuring the sort of late-breaking nasty to his sinker that allowed him to enjoy a lengthy run as one of the top starters in Rockies history. That said, he is a few years removed from his best performances. In the last two years, he is 9-18 with a 5.49 ERA while averaging 20 big league starts per season and about 5 2/3 innings per start. So, the Sox would be betting that the impressive stuff Cook has shown in spring training represents the harbinger of a bounceback, and that the right-hander’s last two years were an aberration.

WHO HAS THE BIGGEST UPSIDE?

There are two ways of approaching this question. Which pitcher, if his stuff clicks as a member of the rotation, has the highest ceiling? And, secondarily, which pitcher, if his stuff clicks as a member of the rotation, would have the greatest impact on the Sox rotation for years to come?

Cook has been an All-Star, so the best-case scenario is fairly well defined. In his best years with the Rockies, he was good for about 200 innings with an ERA around 4.00 that, given the fact he was pitching in one of the worst home environments in the majors at Coors Field, translated to a performance that was roughly 15 percent better than league average.

That said, Cook will be eligible for free agency once again after the 2012 season. As such, he represents either a one-and-done as a member of the rotation for the Sox or, if he is successful, the Sox would have to pay something in the vicinity of market value to bring him back.

It is worth noting that, even though his movement has been consistently excellent this spring, his radar readings have been somewhat inconsistent in his starts this spring. At times, he’s averaged around 89-90 mph in his outings, which would be plenty given the spectacular movement on his sinker; in his most recent outing, he was a tick or two below that, which permits less room for error.

That is a reminder that there is potential value to having him open the year in the minors and controlling his innings in Triple-A in order to permit his shoulder to be at maximum strength over the course of the long haul of the season. If the Sox took such an approach, it would give more time for the team to experiment with other rotation candidates for whom the one-month structure of spring training represents an insufficient look.

If Bard can mix a mid-90s four-seam fastball, a contact-inducing two-seamer, his swing-and-miss slider and turn his changeup -- a pitch that has shown potential as a plus offering in the past -- into a reliable, regular part of his arsenal, he’s the upside guy. Maybe by the middle of 2012, or perhaps by 2013, he could be a legitimate mid-rotation option with the ability to produce outings that are at-times dominant. Moreover, Bard remains under Red Sox team control through the 2015 season. At 26, he has not yet entered a pitcher’s typical prime years.

Aceves doesn’t appear to have the same upside as Bard, given that he’s never been the strikeout-per-inning sort, but his pitch mix is so interesting that it doesn’t seem unreasonable to view him as at least a potential No. 4 or No. 5 starter, with the chance to outperform his stuff based on his tremendous feel for his craft. (Both pitching coach Bob McClure and manager Bobby Valentine rave about Aceves’ pitching intuition.) Aceves will not be eligible for free agency until after the 2014 season. The 29-year-old will remain under team control through his late-prime years.

Doubront’s pitch mix, command and feel also suggest a capable back-of-the-rotation starter whose ceiling might be somewhere between a No. 3 and No. 4 starter. He is also under team control for years to come, as he won’t be eligible for salary arbitration until after the 2014 season, and he won’t become free agent eligible until after the 2017 campaign. At 24 years old, his best years should be ahead of him.

All of that being the case, the two pitchers who could have the greatest long-term impact on the Sox – based on number of years of team control, potential ceiling and age -- are Bard and Doubront.

CAN THE SOX AFFORD TO BET ON UPSIDE?

The Sox are not averse to taking some roster chances on players in hopes of capitalizing on their upside. Some that worked out include David Ortiz (2003), Bronson Arroyo (2004), Dustin Pedroia (2007), Jon Lester (2008) and Alfredo Aceves (2011). All were unproven when they assumed full-time jobs, and all grew to offer immensely impactful seasons and careers. Failed bets included Wade Miller (2005), Wily Mo Pena (2006), John Smoltz and Brad Penny (2009), Jeremy Hermida (2010), and a long line of players that ingloriously and forgettably marched their way out of Boston.

The idea is that the Sox regularly make bets on upside, and expect some to pan out, others to collapse. But in the context of the 2012 rotation, how much risk can the team assume? How many starting spots can be occupied by question marks at the start of the season?

One evaluator suggested that in a world in which a team has four rock-solid rotation members, it’s easy to take an upside gamble with the No. 5 spot. When there are only three such pillars (as is the case for the Sox), the comfort with pursuing upside at the expense of present readiness for the rotation diminishes. That, in turn, would militate against a pitcher like Bard in the rotation, given that he’s an unproven commodity, albeit one with immense upside.

That said, April is a time when there’s a greater comfort level for a team to engage in an extended trial. Because the Sox have three off days in the first 15 days of the season, the damage done by a short start on the bullpen would not be as severe as it would be if it came amidst a 20 games-in-20 days stretch. So, April is a great time to experiment, particularly given that one month of spring training is a somewhat ridiculously limited laboratory in which to try the experiment of converting Bard and Aceves from the bullpen to the rotation.

On the other hand, the Red Sox have a ferocious early season schedule. Of their first 15 games, 12 come against the American League teams that reached the 2011 playoffs. That, in turn, suggests less margin for error and gambling.

A team like the Orioles, that has little hope of contending in 2012, should base its decision based purely on the best long-term outcome. But for the Sox -- a team whose 2-12 start contributed to the team falling one game short of the playoffs in 2011 -- the calculus is different.

Caveat: The Yankees rolled the dice with two rotation spots last year, and turned up a seven. They opted to employ both Bartolo Colon and Freddy Garcia at the back of their rotation, and were rewarded with both good health and strong performances from a pair of former aces.

ARE THERE INNINGS LIMITS OR REASONABLE LIMITS TO EXPECTATIONS OF INNINGS FOR THE PITCHERS?

Of the four candidates, each has workload questions. Bard has never pitched as many as 90 innings in a professional season, and so the Sox might not feel comfortable letting him get too far past the 140-inning mark. Doubront, with a career high of 129 innings pitched as a pro, would likely be restrained to 140-160 innings.

Cook has seen his innings total drop in each of the last three years, reaching 125 frames (between the majors and minors) in 2011. Because he has had shoulder issues in the past two seasons, the Sox would likely need to regulate his innings load.

While Aceves has logged as many as 170 innings in a pro season, that workload took place in 2008. Last year, he threw 122 innings between the majors and minors. Still, because he’s more mature physically than Doubront and Bard, he might not face the same issue of scaled workload bumps that they would.

ARE THE SOX BEYOND THE POINT OF NO RETURN WITH BARD?

Ultimately, the Sox have to do what is right for their club, even if it means bruising some egos in the process. All the same, after Bard spent his entire offseason and spring committing to the idea of starting, the idea of abandoning that experiment is challenging to fathom.

"How," wondered a scout from another organization, "can you pull the plug on him after everything you've talked about this winter?"

The idea of backing away from Bard as a starter after all of four starts – the first two of which were entirely impressive and established him as the odds-on favorite for the rotation, the third of which was messed up by a late-innings entrance and rain delay, the most recent of which was serviceable if unspectacular – seems somewhat ludicrous, particularly given the conventional wisdom that spring training is a terrible time in which to achieve a meaningful evaluation.

Bard is both extremely mature and professional, and so if the Sox decide to shift him back to the bullpen, he’d undoubtedly accept the decision and perform to the best of his considerable abilities. Even so, after the pitcher invested himself so completely in the conversion process and showed some signs -- albeit inconsistent ones -- of making it work, the idea of abandoning the experiment so quickly seems difficult to imagine.

Of course, the Sox could choose to do something like have Bard and Aceves both in the rotation for the first month of the season, see which -- if either -- struggles and then summon Cook from the minors, where he could be waiting in the wings like the cavalry.

THE VALUE OF THE RELIEF ACE

Interestingly, in some ways, Bard is more easily replaced coming out of the bullpen that Aceves. Because Aceves assumed such an unusual workload structure – not only throwing an AL-leading 90 relief innings on top of his four starts, but proving capable of taking on three and four innings of work in a night – a case can be made that he was more valuable than the average reliever. At least that’s how former Red Sox manager Francona and his staff saw it last year, particularly in September, when Aceves threw an incredible 25 innings in relief.

Of course, it’s worth noting that Aceves’ relief value soared in part because the Red Sox pitching staff was so vulnerable. Because the team had so many starts of fewer than six innings, it needed the human bridge that was Aceves. If the starting staff improves, the need for such an unconventional reliever will go down.

Pitching coach Bob McClure noted that the ideal scenario would be to have two pitchers like Aceves -- one for the rotation, one for the bullpen. If Aceves is in the rotation, then there could be some interesting candidates for multi-inning relief roles. Bard has been more than a three-out pitcher; one scout viewed Michael Bowden or even Cook as potentially such a contributor. 

AND WHAT OF THE LOOMING PRESENCE OF DAISUKE MATSUZAKA?

Matsuzaka remains perfectly on schedule in his recovery from Tommy John. He has yet to suffer a setback. He’s shown an impressive mix of pitches in his limited looks. Valentine said this week that Matsuzaka projected to have a return closer to June 1 than July 1.

That, too, could permit the Sox something of a safety net with whichever starters they use in the early season. It also could give the Sox the flexibility to move any of the prospective starters – most notably, Aceves, Doubront or Bard – from the rotation to the bullpen mid-year if the team’s relief proves an area of need, or if/when one of those pitchers is nearing a desired innings cap.

Of course, the idea of assuming that Matsuzaka will be back by early June requires something of a leap of faith in defiance of logic. Nearly all Tommy John rehab processes hit some kind of speed bump, and so even though Matsuzaka’s progression has been flawless to date, the team cannot and does not anticipate with any certainty that it will remain so going forward.

Still, the fact that his return will almost certainly happen at some point in the middle of the season is intriguing, particularly given the potential innings limits that the Sox will impose on the two starters who are in the back of the rotation.

The reality is that the pitchers who start the year in the rotation might well not finish it there, and Matsuzaka is a part of that.

AND THE WINNERS ARE…

The reality is that the decision is complex, with so many variables, that the Sox need to get as much data as possible from the spring (and perhaps beyond) before making it. That is why the coming starts are so critical in the decision-making process.

Based on what’s happened to date, if the Sox go into win-now mode for their rotation, they might be inclined to open with Aceves and Doubront or Cook in the rotation. If they want to try to maximize the longer-term strength of the rotation for the year, they could commit to having, for instance, Bard and either Doubront or Aceves in the rotation to start the year, see who thrives (in particular, whether Bard is on the way to fulfilling his tremendous upside this year) and then bring up Cook towards the end of April as a reinforcement.

Or, if they view the starters as being closely bunched in value, they could allow the shape of the bullpen to dictate their decision, in which case the appeal of having Aceves and Bard – known, dominant quantities – back in relief, or having Doubront as a power lefty with command out of the ‘pen, could rule the decision.

But there is still time for all of the impressions to date to change. Bard could have a dominant outing in which he mixes all three pitches. Perhaps Doubront or Aceves shows some fatigue in his next start, resulting in questions about their fitness for the bullpen. Maybe Franklin Morales and Andrew Miller are unable to ramp up for the start of the season, making Doubront the only left-handed option out of the bullpen.

All of those possibilities reinforce the idea that nothing is set in stone. The Sox are still trying to figure out their pitching staff puzzle, and though they are closer to doing so, more work remains.