  We characterise the Kato property of a sectorial form $\mathfrak{a}$, defined
on a Hilbert space $V$, with respect to a larger Hilbert space $H$ in terms of
two bounded, selfadjoint operators $T$ and $Q$ determined by the imaginary part
of $\mathfrak{a}$ and the embedding of $V$ into $H$, respectively. As a
consequence, we show that if a bounded selfadjoint operator $T$ on a Hilbert
space $V$ is in the Schatten class $S_p(V)$ ($p\geq 1$), then the associated
form $\mathfrak{a}_T(\cdot, \cdot) := \langle (I+iT)\cdot ,\cdot\rangle_V$ has
the Kato property with respect to every Hilbert space $H$ into which $V$ is
densely and continuously embedded. This result is in a sense sharp. Another
result says that if $T$ and $Q$ commute then the form $\mathfrak{a}$ with
respect to $H$ possesses the Kato property.
