【摘要】:In this paper, the authors establish a generalized maximum principle for pseudoHermitian manifolds. As corollaries, Omori-Yau type maximum principles for pseudoHermitian manifolds are deduced. Moreover, they prove that the stochastic completeness for the heat semigroup generated by the sub-Laplacian is equivalent to the validity of a weak form of the generalized maximum principles. Finally, they give some applications of these generalized maximum principles.