In general, there may be many particles with the same amount of energy ε ε . Let the number of particles with the same energy ε ε 1 be N 1 , the number of particles possessing another energy ε ε 2 be N 2 , and so forth for all the possible energies { ε ε i ∣ ∣ i = 1 , 2 , 3 , … … } . To describe this situation, we say that N i is the occupation number of the energy level i . If we know all the occupation numbers { N i ∣ ∣ i = 1 , 2 , 3 , … … } , then we know the total energy of the system. However, because we can distinguish between which particles are occupying each energy level, the set of occupation numbers { N i ∣ ∣ i = 1 , 2 , 3 , … … } does not completely describe the state of the system. To completely describe the state of the system, or the microstate, we must specify exactly which particles are in each energy level. Thus when we count the number of possible states of the system, we must count each and every microstate, and not just the possible sets of occupation numbers.