This thesis intends to examine how prayer is possible, given the indeterminate, unrepresentable, and in some respects unspeakable nature of a supposed “God”. Must one necessarily consent to an identity of the divine, a fortiori a personal one, in order to engage in prayer? Some mystics, such as Eckhart, seem to shake this certainty. The thesis examines the question with two heterogeneous methods: on the one hand, a systematic approach, based on the tradition of so-called "negative" theology, enriched by Bonhoeffer and Tillich, which leads to questioning the attribution of positive or substantial attributes to the divine, but also in dialogue with more recent philosophies, such as that of Levinas; on the other hand, in a more personalized, and almost narrative approach, in the form of a research journal (which claims the legacy of Gabriel Marcel) by trying to account for an experience - of prayer, research, and speculative questioning, in front of an instance of indeterminate address.