Which characterization accurately describes BOTH conduction and convection? Both only occur when currents are created by different densities. Both only occur when currents are created by different densities. Both only occur when there is contact between two solid objects. Both only occur when there is contact between two solid objects. Both can involve solids or gases, and need the presence of insulators in order to occur. , Both can involve solids or gases, and need the presence of insulators in order to occur. Both can involve liquids or gases, and need a temperature difference in order to occur. Both can involve liquids or gases, and need a temperature difference in order to occur.