  Gamma-ray bursts (GRBs) are divided into two classes according to their
durations. We investigate if the softness of bursts plays a role in the
conventional classification of the objects. We employ the BATSE (Burst and
Transient Source Experiment) catalog and analyze the duration distributions of
different groups of GRBs associated with distinct softness. Our analysis
reveals that the conventional classification of GRBs with the duration of
bursts is influenced by the softness of the objects. There exits a bimodality
in the duration distribution of GRBs for each group of bursts and the time
position of the dip in the bimodality histogram shifts with the softness
parameter. Our findings suggest that the conventional classification scheme
should be modified by separating the two well-known populations in different
softness groups, which would be more reasonable than doing so with a single
sample. According to the relation between the dip position and the softness
parameter, we get an empirical function that can roughly set apart the
short-hard and long-soft bursts: $SP = (0.100 \pm 0.028) T_{90}^{-(0.85 \pm
0.18)}$, where $SP$ is the softness parameter adopted in this paper.
