On the surface, the math seems so simple.
Starlin Castro will be 23 in March, and he's signed through 2019 with a team option for the following season.
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Castro is the Cubs' starting shortstop and would appear to have a grip on the position for the next decade.
Javier Baez is the Cubs' top prospect. The 20-year-old was drafted as a shortstop but has Gary Sheffield power. Since the Cubs need a third baseman, nearly anyone you ask adds it up and has the Cubs' top pick in 2011 moving from short to a spot a few feet to his right.
Unless you ask someone with the Cubs.
"That seems to be a common theme," says Cubs boss Theo Epstein. "You just haven't heard anyone in our organization say that because we haven't thought in those terms."
No, the Cubs under Epstein don't make those sorts of decisions until there's a reason to make them, and thus far neither Castro nor Baez has given them a reason.
Castro is still learning, and at the end of last season he made improvements in nearly every facet of the game. But there are still too many moments when he doesn't look like an Epstein-type player on either side of the ball.
Baez, meanwhile, is looking like an even better pick than Jim Hendry and Tim Wilken thought at the time, but conventional wisdom around the game is that Baez isn't a shortstop.
"A lot of what people think is based on what they saw of Javy as an amateur, and people are stubborn in that way," said scouting and player development director Jason McLeod. "I get it because I saw him as an amateur and I thought the same thing, that he's just not quick enough to play shortstop.
"But I was wrong. His instincts are great. His hands are great. His quickness is good enough. His awareness is amazing and his arm strength is a plus. I think he'll continue to progress, but we'll have to wait and see how much he progresses."
So while many continue to project Baez as the third baseman of the future, what if Baez is just as good a shortstop as Castro -- or better -- with a bigger offensive upside?
"It would be a phenomenal problem to have if he gets to the big leagues and is ready to play shortstop," McLeod said. "There's incredible value there in both players."
And the Cubs believe this is a real possibility.
"There's absolutely no doubt in my mind right now that Javy can play shortstop at the major-league level," McLeod said. "This kid can make every single play you need to make at shortstop at the big-league level.
"He can go to his left, he can go to his right, and he has the arm to make any play. He has the quickness.
"The reason people think he's not a shortstop is we have a shortstop. They see the big body type (6-1, 205) and they automatically think he's a third baseman or another position. There have been a lot of guys his size who have played the position well defensively."
Off the top, one thinks of even bigger players like Cal Ripken (6-4, 200) and Troy Tulowitzki (6-3, 215).
"Obviously, we're not comparing him to any Hall of Famers right now, but size-wise, yes, you think of certain guys," McLeod said. "Javy can play the position very, very well, and if he hits like you think he will, why would you talk about moving him off shortstop?"
Of course, you wouldn't put it past an Epstein-run organization to try to sell a player's qualities to increase the market value of both Castro and Baez.
"You don't have to sell Javier Baez," McLeod laughed. "Go watch him play. Just go watch him play. The kid can play shortstop, and he's so young.
"For anyone who doesn't think he can play major-league shortstop, they just haven't seen him play the position. He's a very talented kid who hasn't even played a full season yet in pro ball."
Cubs fans will get to see some of Baez as a nonroster invite to spring training this month, but he will head back to high Class A Daytona to begin 2013 and could move quickly to Double-A Tennessee with a good start.
But after Baez had a .979 OPS at Peoria (A) last season in 213 at-bats, he hit only .188 at Daytona in 80 trips to the plate.
"He's played only three months in the minors, so this is a big season for him," McLeod said. "We'd love to see him play 120 or 130 games this year.
"There's pressure on him. Everyone knows him and all the major publications are talking about him.
"He's got all the skills. Let me be clear about that: He's got all the skills. But he's got a lot of work to do to get to Wrigley Field."
If he gets there as a shortstop, that will make for one of the more interesting decisions in recent Cubs memory.
But as McLeod said, and as problems go, that would be a pretty nice one to have.
•Hear Barry Rozner on WSCR 670-AM and follow him @BarryRozner on Twitter.