We really need to make this system self-explanitory.
That number you saw getting smaller were the amount of points you had to spend on doctrines.
T4= 4 points spent, T3= 3 points spent, etc. etc. You only have 13ish on the top 3 rows to spend, and to get a T4 you must choose the t3,t2 and t1 in front of it.
13 points
tier 1>tier2>tier3>tier4
tier 1>tier2>tier3>tier4
tier 1>tier2>tier3>tier4
9 points
tier 1 tier2 tier3
tier 1 tier2 tier3
tier 1 tier2 tier3
Basically the top row are progressive unlocks requiring the previous one to be unlocked, and a certain level to unlock
the bottom row however can be chosen in any order, if you meet the level requirements