Three Dialogues in Opposition to Skeptics and Atheists is a supplement to George Berkeley`s Treatise Concerning the Principles of Human Knowledge. In Three Dialogues Berkeley wrestles with the nature of the soul and of God through a series of three conversations between Hylas and Philonous. George Berkeley was an Anglo-Irish philosopher whose primary achievement was the advancement of a theory he called "immaterialism". This theory denies the existence of material substance and instead contends that familiar objects like tables and chairs are only ideas in the minds of perceivers, and as a result cannot exist without being perceived. Thus, as Berkeley famously put it, for physical objects "esse est percipi" ("to be is to be perceived").