"In 1600-1800, the soliloquy really functions to undermine the speaker." How convincing is this statement?
Given the ambiguity of the word “undermines” and the anonymity of the source of this quotation, and questioning the dates 1600-1800 as somehow bracketing a dramatic device, answering this question becomes difficult. Let us say that the dates are meant to include Elizabethan and Jacobean drama (and perhaps the Carolinian drama) up to the Interregnum. In this period, drama was very popular, and the soliloquy universally employed; its primary use, according to literally all scholars of the period, was to give voice to the thoughts of the speaker, honest thoughts uncamouflaged by social needs—caution, prevarication, guile, etc.—so that the audience (the readers of the texts were a secondary market) could weigh his thoughts against his actions and his reactions to the actions of others. If the question is suggesting that soliloquys undermine the dramatic posture, the “public face” of the speaker in a social situation, that may well be, but only as a secondary function. It is often the repository of the playwrights’ best poetry, imagery, and metaphors, because it is not “heard” by the other characters. Another possibility is that the stater of the suggestion is pointing out a change in the soliloquy’s function from the Elizabethan era to the Jacobean period. Many changes in tone, style, dramaturgy, and content have been documented after Queen Elizabeth’s death—notably, an increase in rawness and bloodiness, due not only to a change in the court but also due to an increasing call for sensationalism in the jaded Jacobean audience.