Modern systems are heterogeneous, geographically distributed and highly dynamic since the communication topology can vary and the components can, at any moment, connect to or detach from the system. Service Oriented Computing (SOC) has emerged as a suitable paradigm for specifying and implementing such global systems. The variety and dynamics in the possible scenarios implies that considering such systems as belonging to a single architectural style is not helpful. This considerations take us to propose the notion of Mode as a new element of architectural descriptions. A mode abstracts a specific set of services that must interact for the completion of a specific subsystem task. This paper presents initial ideas regarding the formalization of modes and mode transitions as explicit elements of architectural descriptions with the goal of providing flexible support for the description and verification of complex adaptable service oriented systems. We incorporate the notion of mode to the Darwin architectural language and apply it to illustrate how modes may help on describing systems from the Automotive domain.