In the isospin picture, the four Deltas and the two nucleons were thought to simply be the different states of two particles. The Delta baryons are now understood to be made of a mix of three up and down quarks – uuu (Δ), uud (Δ), udd (Δ), and ddd (Δ); the difference in charge being difference in the charges of up and down quarks (+ ⁠ 2 / 3 ⁠ e and − ⁠ 1 / 3 ⁠ e respectively); yet, they can also be thought of as the excited states of the nucleons.