MINNEAPOLIS -- Deciding whether Sam Bradford will start at quarterback for the Minnesota Vikings on Sunday appears to depend on how quickly he can run the team's offense at a workable level.

There's not much mystery about whether the Vikings want to put Bradford on the field soon. As Tennessee Titans coach Mike Mularkey said Wednesday, like a man calling the bluff of a card player across the table, "They wouldn't give up a [No.] 1 and a [No.] 4 [draft pick] to have him sit very long." But what the Vikings want to do and what they can manage in the days before their season opener at Tennessee are different things.

It seems, then, that we should spend a minute or two discussing what NFL teams mean when they talk about the challenge of learning a system. At a base level, there's plenty of shared material in different playbooks; there are only so many routes an NFL team can run. The minutiae behind those routes, though -- the language used to call them, the depth at which they're run and the adjustments they take on against different coverages -- is the secret sauce that make one team's offensive recipe different from another. And those are the things that take time to learn.

Wide receiver Charles Johnson said "how things are called" is the biggest difference between systems.

"Some people have concept-based systems. We've got numbers, with a little bit of concepts here," he said. "I'm sure Sam has been in both styles of offense. He's picked it up well so far."

What does Johnson mean by numbers versus concepts? It has to do with how routes are communicated in a play call. In the Air Coryell system that Vikings offensive coordinator Norv Turner has used to great effect in his career, routes are assigned a number from 0-9, with larger numbers generally corresponding to routes that break farther down the field. A "9" route is a go route. An "8" route -- as in the famous "Bang 8" play from Turner's days as Dallas Cowboys offensive coordinator -- refers to a post route. A "7" route is a corner route. And so on.

The other popular school of thought, usually associated with the West Coast offense, generally requires quarterbacks to call out each route concept by name in a play call, which leads to more terminology and requires more memorization. As Johnson said, the Vikings primarily use numbered routes, but they have a few wrinkles that include names of route concepts. Bradford is on his fifth coordinator in his seventh season in the league, and he has played in everything from Air Coryell and West Coast schemes to Chip Kelly's spread offense. On some level, he has a broad enough exposure to different ideas that he won't encounter much that is new to him.

The presence of Pat Shurmur -- Sam Bradford's offensive coordinator in St. Louis and Philadelphia -- on the Vikings' staff has been comforting to the recently arrived QB. AP Photo/Jeff Roberson

"Sam's been in this league a long time," Johnson said. "I say it all the time: The NFL is a copycat league. If you've seen somebody run a '4' route, it's a '4' route. You know what a curl route looks like. He's been around football long enough. He knows what a curl route looks like. He's just got to get used to how we call the plays, our depths, all that kind of stuff."

One thing Johnson mentioned, though, can only be mastered with repetitions in practice: NFL teams tell receivers to break on their routes at different yardage markers, which means quarterbacks have to develop a feel for the specific timing with each receiver on each route. It's why you often hear QBs talk about the value of offseason work with their receivers, and why Bradford's task this week is as much art as it is science.

"Obviously, it's not ideal," Bradford said. "Normally you have an offseason. You have a summer to at least work on some of that timing, but I just think that means that every rep we get in practice is more important. We've got to be focused. I've got to be focused. We've got to take advantage of every throw in practice, get throws after practice and make sure that we're all on the same page."

The presence of Vikings tight ends coach Pat Shurmur, who was Bradford's offensive coordinator in both St. Louis and Philadelphia, has helped some, Bradford said.

"He's not the quarterback coach here, so it's a little bit of a different role, but just having that familiar face -- someone that, if I do have questions and I need to refer to an old language, I can go up to Shurm and say, 'Hey, can you kind of explain this in terms that we've done in the past?'" Bradford said. "In that regard, Shurm's been awesome."

All of this explains why Bradford's task is so tall this week. In addition to learning the Vikings' playbook and developing timing with his receivers, he has had to get a grasp of protection calls, checks at the line of scrimmage and variations his receivers might run based on the coverage they see. It's not so much akin to quantum physics as it is something more practical, like becoming at least conversational in a foreign language.

In a week.

"Normally, when you go into a game week, you already have a pretty good grasp of what you're doing offensively," Bradford said. "You spend a lot of time studying the opponent and what they're doing on defense. It's been a little more difficult than it normally is, because as much as I'm trying to study Tennessee, I'm probably studying even more of our playbook, making sure I'm comfortable with what we're doing offensively."