  In the present paper we prove the compactness theorem with respect to partial
structures and quasi-truth, using the technique of ultraproducts. Partial
structures and quasi-truth are two notions developed within the partial
structures approach, which is a philosophical conception that emerged in the
context of contemporary philosophy of science. Nevertheless, the notions
developed within this conception, in particular the two mentioned, have a
model-theoretic content that has not been explored so far, so that this paper
is part of a project where we intend to analyze their formal properties by
means of the development of a partial model theory, which is an extension of
traditional model theory to partial structures.
