Let X be a normal complex projective variety, T ⊆ X a subvariety, a : X → A a morphism to an abelian variety such that Pic 0 (A) injects into Pic 0 (T ) and let L be a line bundle on X.Denote by X (d) → X the connectedétale cover induced by the d-th multiplication map of A, by T (d) ⊆ X (d) the preimage of T and by L (d) the pull-back of L to X (d) . For α ∈ Pic 0 (A) general, we study the restricted linear system |L (d) ⊗ a * α| |T (d) : if for some d this gives a generically finite map ϕ (d) , we show that ϕ (d) is independent of α or d sufficiently large and divisible, and is induced by the eventual map ϕ : T → Z such that a |T factorizes through ϕ.The generic value h 0 a (X |T , L) of h 0 (X |T , L ⊗ α) is called the (restricted) continuous rank. We prove that if M is the pull back of an ample divisor of A, then x → h 0 a (X |T , L + xM ) extends to a continuous function of x ∈ R, which is differentiable except possibly at countably many points; when X = T we compute the left derivative explicitly.In the case when X and T are smooth, combining the above results we prove Clifford-Severi type inequalities, i.e., geographical bounds of the form vol X|T (L) ≥ C(m)h 0 a (X |T , L), where C(m) = O(m!).