  In 1959, F.Galvin and B.Jonsson characterized distributive sublattices of
free lattices in their paper. In this paper, I will create new proofs to a
portion of Galvin and J\'onsson's results. Based on these new proofs, I will
explore possible generalizations of F.Galvin and B.J\'onsson's work by defining
\emph{spanning pairs} and proving partial results which may help with analysing
finite width sublattices of free lattices; and by making some new observations
on finitely generated lattices over semidistributive varieties.
  The work done in this paper may assist in attacking the following
long-standing open problem: Which countable lattices are isomorphic to a
sublattice of a free lattice?
