An algebra $𝒜=(A,F)$ is subregular alias regular with respect to a unary term function $g$ if for each $\Theta ,\Phi \in \text{Con}𝒜$ we have $\Theta =\Phi$ whenever ${\left[g\left(a\right)\right]}_{\Theta }={\left[g\left(a\right)\right]}_{\Phi }$ for each $a\in A$. We borrow the concept of a deductive system from logic to modify it for subregular algebras. Using it we show that a subset $C\subseteq A$ is a class of some congruence on $\Theta$ containing $g\left(a\right)$ if and only if $C$ is this generalized deductive system. This method is efficient (needs a finite number of steps).