Profound intellectual disability, the most severe form of intellectual disability, has long been left at the margins of philosophical thought. Further, many accounts of the grounds for human moral standing rely on the possession of higher-order capacities of mind that serve as status-conferring attributes to the exclusion of human beings with more significant intellectual impairments. This dissertation advances three main theses responding to three main questions regarding the lives of those with profound intellectual disability. First, with regards to the question of how we should conceptualize profound intellectual disability, that we should think about it as a disability characterized by the impossibility of successful, mutual linguistic communication rather than solely as extreme cognitive deficit. Second, with regards to the role of heterogeneous forms of communication that are available to non-speaking intellectually disabled persons, that there is ubiquitous form of communication I call relationship-constituted and constituting meaningful expressions (RCMEs). RCMEs are morally significant in their relying on the fabric of a particular relationship for their use, and they are particularly salient for pairs of profoundly intellectually disabled and non-intellectually disabled communicators. Third, with regards to human moral standing and the historical philosophical exclusions of intellectually disabled lives, that the grounds for human moral equality lie in our ability to employ RCMEs to develop and deepen relationships – a capacity whose possession in one individual presupposes its existence in others.