Indirect metaphors are pervasive in everyday language: People talk about "long" vacations, "short" tempers, and "colorful" language. But, why do we use concrete lexical items that are associated with the physical world when we talk about abstract, or non-physical, concepts? A potential answer is provided by proponents of Conceptual Metaphor Theory (CMT), who propose that only a small set of the concepts which make up our conceptual system emerge directly from physical experience, and it is this small number of concepts that serves to structure the ways in which we think and talk about abstract concepts (Lakoff & Johnson, 1980). This key assumption in cognitive linguistics--that our understanding of concrete concepts serves to ground our understanding of abstract concepts--is the focus of my research. Although indirect metaphors are thought to be the result of grounded conceptual connections, motivated by experiential knowledge and flowing from the physical to the non-physical (Grady, 1999), it is unclear whether people access these grounded connections when processing the meanings of indirect metaphors. The prepositions "in" and "on" are an interesting test case for grounded connections: Both lexical items are used frequently by speakers not only to identify the location of one object relative to another but also to refer to more abstract relationships. Therefore, I experimentally investigated the possibility that grounded connections are available for use in tasks requiring on-line processing of these prepositions: Would participants make use of conceptual connections, and if so, would the characteristics associated with these conceptual connections be consistent with the CMT grounding assumption? Although the results for "in" were consistent with the CMT grounding assumption, the results for "on" were not. In fact, differences between "in" and "on" were found throughout stimulus development, and these differences were used to help explain this discrepancy. The patterns observed throughout this dissertation suggest that "in" may be more metaphorically active than "on," meaning that "in's" potential to participate in indirect metaphors is higher than "on's," and that one consequence of this higher metaphorical activity is an increase in the availability of grounded connections during on-line processing. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]