This paper reports on the analysis of thirty two research articles written in Spanish in the fields of education, linguistics, philosophy and psychology, with the purpose of identifying writers’ choices of modality and modal commitment. The objective was to find out how disciplinary discourse varies across disciplines in the humanities with respect to the use of possibility, probability, obligation, inclination and quantity, along the dimensions of knowledge about the discipline, the research process and text organization. The analysis shows high modal commitment in most disciplines studied, but important differences are found as far as use of the signals used and the type of knowledge referred to.