Models for granitic melt viscosities reveal the influences of H2O, temperature and tectonics on melt segregation, ascent and emplacement. Low-T magmas are wetter than those formed at high-T, so log10 melt viscosity (Pa s) is 3.2-6.3 for leucogranite to tonalite, only 10-1000 times more viscous than basalts. There should be no correlation between critical dyke width (to prevent freezing) and tectonic setting. Granitic magma ascent rates in dykes vary by <10%, and melt extraction rates should be similar in different settings. Emplacement styles are not predetermined by composition or temperature, but by local structures and tectonics.