Get your popcorn ready, film's biggest night is just around the corner. That's right, the 2017 Oscars will finally arrive on Sunday, Feb. 26 for their 89th annual run. But before you start casting your predictions for who will take home the year's top honors, you may want to start with a simpler question: do you know the difference between supporting and leading actor at the Oscars?

If you don't, that's OK — the lines are pretty blurry. In fact, the Supporting Actor and Actress categories weren't even introduced until 1937 — eight years after the Oscars made their debut. Up until then, there was only a Best Actor and a Best Actress award, and they were given to whoever was deemed the best actor in any role that year. But they later decided to add Supporting Actor and Actress in order to allow for more winners and honor a wider range of talent.

That means the Academy had to find a way to differentiate between these categories, and according to the International Business Times, "leading roles" were loosely decided by which actors had about the most screentime of all the performers in a film. That's not quite a precise definition, and 80 years later, it's still far from an exact science. According to the Academy Awards' official list of rules, "The determination as to whether a role is a leading or supporting role shall be made individually by members of the branch at the time of balloting," which basically means that the Academy voters get to decide and doesn't really help to clear things up.

It seems there's confusion behind scenes, too. The rulebook also states that, "If any performance should receive votes in both categories, the achievement shall be placed only on the ballot in that category in which, during the tabulation process, it first receives the required number of votes to be nominated," which means that it's totally possible for an actor to be considered in both categories, though they'll only make the official nomination list for one.

Still, there can be some assumptions made based on screentime and the nature of the part. If there's a central character, for instance, the Best Actor nomination would likely go to them, while movies with ensemble casts may require a little more discussion.

Let's look at the 2017 Oscar nominees as an example. Many of the actors nominated in the Leading Role categories played the protagonists in their respective projects: Natalie Portman in Jackie, Casey Affleck in Manchester by the Sea, Ryan Gosling and Emma Stone in La La Land. Moonlight, on the other hand, unfolded across three chapters with different actors playing the same character throughout. There wasn't one single person driving the film, so it makes sense that its stars were nominated in the supporting categories.

Things get murkier, however, with Lion. Dev Patel led brilliantly as the emotionally tortured Saroo Brierely, but was ultimately nominated under Best Supporting Role. Australia's SBS theorized that this stemmed from some strategic jostling from producers — not uncommon for awards shows — as Patel may stand a better shot at winning outside of the Ryan Gosling-Casey Affleck stand-off for Best Actor.

Basically, there aren't any concrete rules that define a Leading performer from a Supporting one. It's really just a judgment call. So don't worry, the Academy is just as confused as you.

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