Possessive manaism is the belief that mana is ‘attached’ to an individual, so that one cannot merely use physical means to extract mana from them. According to this belief, each person has a certain amount of mana associated with them at any given time, and when they obtain mana, that mana ‘comes into their possession’ rather than remain associated with the object or other source from whence it’s derived. Without possessive manaism then, one must transport objects believed to hold mana, and that mana can be given to another by physically giving them the object holding the mana; and for certain types of mana such as aer mana, the mana can only be held temporarily before it dissipates.
Once a person has mana associated with them, the mana remains with them and collects in a “mana pool”, so they act as a personal mana battery. They can then use that mana directly to work spells.
In its weak, or unlimited, form, there is no limit to the amount of mana that each person may possess. This is the form that is then used in monetary manaism. (Remember, in its nonexistent form, there is no mana necessary and hence no limit to the amount of it.)
In its intermediate, or variable, form, each person has a limit that can be enhanced through practice spellworking.
In its strong, or fixed, form, each person has a limit on how much mana they may possess at any one time. This limit would be different for different people, and the more a person experimented with working spells the more they would know what their limit was.