Implicit invocation (II) and aspect-oriented (AO) languages 
provide related but distinct mechanisms for separation of 
concerns. II languages have explicitly announced events  
that run registered observer methods. AO languages have 
implicitly announced events  that run method-like but more 
powerful advice.  A limitation of II languages is their 
inability to refer to a large set of events succinctly.  
They also lack the expressive power of AO advice. Limitations 
of AO languages include potentially fragile dependence on 
syntactic structure that may hurt maintainability, and 
limits on the available set of implicit events and the 
reflective contextual information available. Quantified, 
typed events, as implemented in our language Ptolemy, solve 
all these problems. This paper describes Ptolemy and 
explores its advantages relative to both II and AO languages.