Choosing the right abstractions is important for managing the complexity of your system. Three important abstractions used today are object, component and agent. Many similarities exist between these abstractions, but to make proper use of each, one should have a good understanding of their differences. Too often, we hear people discussing their agent-based systems when they have simply used the object abstraction. In this conceptual paper, we use communication as a means to differentiate the three abstractions. We describe communications patterns for each abstraction using an abbreviated pattern format, identifying the contexts, forces and solutions to different problems that present themselves for each abstraction. Our objective is to help developers identify the abstractions they are working with so they can make better use of them.