Ontology,epistemology and axiology construct the philosophical core,while methodology links epistemology to ontology. Epistemology determines methodology and guides sciences. There are three paradigms in sciences,and science is characterized by logic,verifiable and quantitative properties. Since Library and Information Science (LIS) belongs to sciences,it matches the three characteristics. The article is organized by a logic chain from philosophical views,scientific philosophical paradigms to LIS approaches,in which the author contributed the 2S2R model for guiding research and suggested “generalized double verification” for integrating qualitative and quantitative methods,theoretical derivation and practical verification. Once that double integration becomes a methodological principle,the qualitative and quantitative methods can be unified. This paper is a methodological exploration of LIS theories. 2 figs. 1 tab. 18 refs.