In Brazilian Jiu-Jitsu, belt promotions are subjective — there is no set criteria to earn a belt. This doesn't mean there aren't criteria. If size, strength, and age are equal you should expect more senior belts to be able to consistently submit lower belts. But how do they do it? The answer to that question will give you an idea of the belt criteria and what you should be working on to earn your next belt.
Groundsworks holds belt promotions twice per year. Before belt promotions, instructors will spar with you, tell you what you need to work on over the next 6 months, and tell you whether or not you are getting promoted.
There are only four color belts in Jiu-Jitsu. You may spend several years at each rank, so it's best not to focus too much on getting promoted and instead focus on getting better than you were yesterday, last week, last month, etc.
How each belt rank defeats lower ranked opponents
Blue Belt (Faixa Azul)
Blue Belts understand all of the basic positions in Jiu-Jitsu. They know a couple techniques from each of those positions and can perform them successfully against resisting opponents. Most importantly, Blue Belts have learned how to escape from bad positions. As white belts they spent a lot of time in the bottom position with their opponents mounted, in side control, and in back control. Out of necessity, they learned to defend submissions and escape bad positions. Blue belts beat white belts because they know techniques white belts don't and have a deeper understanding of techniques than white belts do.
Purple Belt (Faixa Roxa)
Purple Belts chain techniques together and attack their opponents in a systematic way so that the opponents' defense leads them into the Purple Belt's next attack. As Blue Belts, they added a lot of techniques to their arsenal and have identified favorite techniques that fit both their body type and personality. While Purple Belts are familiar with all guard and passing styles, they typically specialize in just a few styles. While Blue Belts typically wait for openings to use a technique, Purple Belts beat their opponents by creating those openings.
Brown Belt (Faixa Marrom)
Brown Belts have refined their technique to such a degree that they do not need to rely on their physical attributes (size, strength, speed). Because they rely less on their physical attributes, bigger/faster/stronger opponents are less problematic for them than they are for Purple Belts. If they aren't lifting weights outside the gym, they are usually physically smaller than they were at purple belt because they rarely muscle technique.
Brown belts are very advanced practitioners and are capable of directing much of their own training; they can effectively teach and troubleshoot the their core techniques. They beat Purple Belts by being more efficient and by having a more nuanced understanding of technique.
Importantly, Brown Belts represent the academy and are leaders in our community. When Purple Belts are being considered for promotion to Brown Belt, their character on and off the mat is taken into account. This is not the case for all gyms, but it is for Groundworks.
Black Belt (Faixa Preta)
Black Belts have a deep understanding of all techniques, not just the techniques they use. They are exceptionally good at setups — they recognize that all setups start with the first point of contact, usually a grip, so it's common to see them fight for and insist on getting the grips they want.
As Brown Belts they spent a lot of time refining their game and looking for techniques and adjustments that fill in the gaps in both their defense and offense. They likely spent time teaching and learning how techniques work with different body types and ability levels. Black belts understand the principles behind why techniques work and are capable of troubleshooting techniques and positions they've never seen before. Most importantly Black Belts can teach all of the core techniques of Jiu-Jitsu and can help advanced students level up their games.