Abstract : In this paper, we introduce closure operators $[\cdot]_c$ and $[\cdot]_a$ on a space and study some relations among $[\cdot]_c$, $[\cdot]_a$ and countable tightness. We introduce the concepts of a strongly sequentially closed set and a strongly sequentially open set and show that a space $X$ has countable tightness if and only if every strongly sequentially closed set is closed if and only if every strongly sequentially open set is open. Finally we find a generalization of the weak Fr\'echet-Urysohn property which is equivalent to countable tightness.
