I know that for the RK2 method to be consistent we must have $a + b = 1$ in the following equation
$\begin{aligned} y_{i+1} &= y_i + h(ak_1 + bk_2)\\ k_1 &= f(x_i, y_i)\\ k_2 &= f(x_i + \alpha h, y_i + \beta hk_1) \end{aligned} $
However, for the general $s$-stage Runge-Kutta method, what conditions must one have on the terms in the Butcher tableau in order to ensure consistency?