### Abstract:

In this dissertation, I propose a model for comparing the degree to which diatonic major and minor keys are related to one another. I consider specific tonal and interval relationship factors (e.g., circle-of-fifths distance, tonic-to-tonic interval class) and their influence on the perception of how two keys are related. For all forty-eight possible relationships of two diatonic keys, I assign numerical values for each factor. These values are based on theoretical concepts where appropriate (e.g., the number of steps between the keys on the circle of fifths) and on an intuitive assessment in cases where there is no accepted numerical designation (e.g., the direction along the circle of fifths one travels from the first key to the second). I weight the values according to the relative significance of each factor and sum the weighted values to obtain a single numerical measure that describes the "distance" from the first key to the second. This abstract idea of distance represents the degree of relatedness between two keys. Larger distance values denote a lesser degree of relatedness. The model incorporates the idea of keydistance asymmetry - that the perceived distance between two keys depends on the order in which they occur.I devote one chapter to a general discussion of key relationships and another to the application of the model as a tool for analyzing the harmonic structure of tonal compositions from the standard literature. Using the key-distance model I develop in Chapter 2, I also provide a harmonic analysis of a composition for symphonic band which I have written to complement the theoretical portion of this dissertation. The score of this piece is included as an appendix.