In my opinion: Step 1: At 2 years old we were all fluent speakers Step 2: Light stutterer: Then we taught ourselves that speech errors are a problem and to be avoided, and that speech is difficult to do and needs effort - causing a speech block (sometimes in combination with e.g. an ear infection reinforcing this process) Step 3: Medium stutterer: Then in order to prevent (or avoid) blocks, we started doing repetitions. The positive effect was that we hold the listener's attention by doing repetitions. In this theory 'repetitions' are not primary but secondary behaviors. Step 4: Heavy PWS: if 'repetitions' make you look flawed, then you start to adopt a new condition to avoid repetitions by being in a speech block. The positive effect is: the visible stutter doesn't look 'weird' anymore and by being in a speech block for a long time, you prevent multiple stutters Conclusion: So, in my viewpoint our core (behavioral) stutter is a speech block. Repetitions are just a side-effect (secondary behavior). Also, as explained - both repetitions as well as speech blocks are caused by blaming reasons like: * anticipation * fear Blaming these reasons then result in not moving our mouth or not breathing out (Dr. Parry calls it a valsava manouvre where we tense our abdominal muscles and instead he urges PWS to relax it)