We argue here that models of SN Ia based on gravitational collapse wit
h the ejection of only a small amount of matter and nickel will be sub
luminous, and are likely to have problems with the light curve and esp
ecially with the spectral evolution, Canonical thermonuclear explosion
models can account for the light curves not only in the optical but i
n the IR and for the spectral evolution, Some classes of thermonuclear
models can give adequate kinetic energy of expansion with a range in
nickel mass, thus accounting for both normal and subluminous SN Ia. Th
e subluminous models may form interesting amounts of CO in the ejecta.
We discuss the comparison of SN Ia,b, and c. SN Ia have an ejecta ric
h in high opacity iron. SN Ic have comparable ejecta mass, and somewha
t lower opacity C/O dominated ejecta. SN Ib probably have the highest
mass, but are composed largely of low opacity He. We argue that SN Ic
are very deficient in both H and He, but that SN Ib may have small, bu
t detectable, amounts of H in their outer layers. There is general agr
eement that some form of convection is critical for proper understandi
ng of the explosion mechanism of gravitational collapse. There is stil
l a healthy debate about how the convection proceeds and whether it is
the universal cure.