They could be treated as the same particle, with the difference in charge being due to the particle being in different states. Isospin was introduced in order to be the variable that defined this difference of state. In an analogue to spin, an isospin projection (denoted I 3) is associated to each charged state; since there were four Deltas, four projections were needed. Like spin, isospin projections were made to vary in increments of 1. Hence, in order to have four increments of 1, an isospin value of ⁠ 3 / 2 ⁠ is required (giving the projections I 3 = + ⁠ 3 / 2 ⁠, + ⁠ 1 / 2 ⁠, − ⁠ 1 / 2 ⁠, − ⁠ 3 / 2 ⁠). Thus, all the Deltas were said to have isospin I = ⁠ 3 / 2 ⁠, and each individual charge had different I 3 (e.g. the Δ was associated with I 3 = + ⁠ 3 / 2 ⁠).