This book is about the mental model theory. However, it does not focus on the habitual uses of it by its proponents. Those uses refer to accounts of several cognitive activities. But the present book tries to utilize that theory in other ways already indicated (although not completely developed) by the author in the past. Thus, its aims are basically three: 1) To show that essential elements of the theory can offer keys to build qualitative research methods. 2) To argue that some of its most important assumptions can help recover deep syntactic structures in sentences. 3) To describe how the reconstruction of the thought of ancient philosophers can also give evidence in favor of frameworks such as the mental model theory. The adherents of the theory do not often consider these different uses. Nevertheless, the author of this book has pointed them in previous works and, based on those works, tries to delve into them here.