Published online by Cambridge University Press: 12 April 2016
A unified picture is presented for the formation of bars in galaxies of different morphological types based on a simple model of the growth of galactic disks by gas infall from haloes. The infall timescale is found to be a key parameter which determines the dynamical property of the resulting disk. It is suggested that the bars in early-type disk galaxies have been formed in tidal interactions with other galaxies whereas those in late-type galaxies formed spontaneously due to gravitational instability (bar instability) in their disks.