The Clean Architecture book clarifies SRP (p.62):

> Historically, the SRP has been described this way:
> 
> *A module should have one, and only one, reason to change.*
>
> Software systems are changed to satisfy users and stakeholders; those users and stakeholders *are* the "reason to change" that the principle is talking about. Indeed, we can rephrase the principle to say this: 
>
> *A module should be responsible to one, and only one, user or stakeholder*
>
> Unfortunately, the words "user" and "stakeholder" aren't really the right words to use here. There will likely be more than one user or stakeholder who wants the system changed in the same way. Instead, we're really referring to a group-- one or more people who require that change. We'll refer to that group as an actor. 
>
> Thus the final version of the SRP is: 
>
> *A module should be responsible to **one**, and **only one**, actor.*