There exists $x \in \mathbb{R}$ such that $x^2 \leq 0$

For some $x \in \mathbb{R}$, $x^2 = 0$

For all $x \in \mathbb{R}$, $x^2 \leq 0$

There exists $x \in \mathbb{R}$ such that $x^2 < 0$