Here the pen is not an agent or a patient: it is not acting itself or being acted on by an agent. What about the highlighted noun phrase in the next example? What kind of role in the situation does it express? These noun phrases do not have the role of agent, but rather the role of experiencer: the individuals identified by these phrases are experiencing feelings or sensations.
Although we have changed an active clause into a passive one, and the boat is now the Subject, nothing has changed in the real world. Who or what is the agent in the following clause? So John is the agent in the following example: The agent is the ‘doer’ of an action described by a ‘doing’ verb. The most obvious semantic role is called the agent. These people and things are referred to by the parts of the clause in a way that tells us what their roles are. They concern the roles that people and things play externally, in the real world. The terms Subject and Object are called functions: they explain the grammatical role played by a particular element in the clause.
We might also say that John is the Subject and the boat is the Direct Object of the clause (or sentence in this case). More specificallty, we say that it is a verb in the past tense. We can say that steered in the following example has a grammatical form, namely verb. When we talk about grammar, we mostly discuss language from the point of view of its internal characteristics.