Soliloquy is a significant symptom in schizophrenia and is usually regarded as being related to auditory hallucination. Elucidation of the psychopathology of soliloquy is incomplete. Soliloquy is also a normal human behavior that has multidimensional functions such as guiding internal cognitive processes and managing social interaction. In the young, soliloquy appears as egocentric speech and arises before maturation of the third-person perspective. Soliloquy has been regarded as indicative of an intermediary stage during the transformation of social speech into internalized thinking. Every thought process retains a social dimension because language itself is based on intersubjectively shared meanings, and internal thinking originates from interpersonal communication. Thus, soliloquy can be seen as a kind of thought process that accentuates the social dimension. This approach may help in understanding soliloquy in normal and pathological situations. Soliloquy was actively discussed in the late nineteenth and early twentieth century in European psychiatry. Since then it has received less attention and has been neglected as an academic concern, except in child developmental theory. Recently however, soliloquy has attracted more attention among neuroscientific researchers. To attain an advanced understanding of soliloquy, it is necessary to integrate the early European perception of soliloquy with current developmental theory. In this paper, we review past literature on the conceptualization of soliloquy and integrate those concepts into an explanatory framework. In addition, a case series and a discussion of the applicability of the explanatory framework are presented. Our results may help provide an insight into the contemporary understanding of soliloquy.