This article highlights some basic aspects of the Systemic Functional Grammar described by Halliday (1984 and 1994)]and his followers; we intend to analyze the modalization in the construction of discursive strategies in MA dissertation introductions. The corpus is composed of 10 MA dissertation introductions with emphasis in the arguments for the research, which are reinforced by the constant occurrence of NECESSITY JUSTIFICATION and AIMS OF THE RESEARCH. We adopt the methodology called case study; therefore we analyze a specifi c discourse community and, for this, we used the software Wordsmith Tools (Scott, 1996), a device that allowed us to analyze in a detailed manner the lexical items from the texts. The analysis of our corpus showed that, at the Program in Applied Linguistics and Language Studies of PUC-SP, modalization is frequently used through modal verbs in the excerpts called NECESSITY JUSTIFICATION and AIMS OF THE RESEARCH.