Impulsive waves are the thing every trader that uses Elliott wave theory is looking for. More exactly, out of the five waves the impulsive move it is formed, the third one is the most searched for, looked for, desired, hunted, etc. That is because an impulsive move has to respect some rules, and one of the rules states that at least one wave in an impulse needs to be extended.
We already covered extensions on the 3rd chapter when talking about the Fibonacci extension tool. An extension in an impulse means 161.8% out of the previous wave. Subject to expansions are wave 3, wave 5 and wave 1, in this order. Most common is for the third wave to be extended, and this is most likely 161.8% extension projected from the length of the 1st wave. Second most likely is for the 5th wave to be extended, and in this case the extension goes 161.8% out of the length of the 3rd wave. And third, 1st wave might be extended but then the whole structure would probably take the form of an ending diagonal, where the first wave usually is the biggest.
Another important rule for an impulsive wave is that the third wave can never be the shortest one. If you have count, regardless if to the upside or to the downside, and the third wave is the shortest one, than that is not an impulse. Also, if no wave out of a five wave sequence is extended, than that is not an impulsive move either.
The recording coming with this sub-chapter illustrates impulsive moves and what makes an impulse being an impulse, meaning analyzing conditions to be looked for: extensions, principle of alternation between the corrective waves, length of the waves, etc.
Book recommendation: Robert Balan, Elliott Wave Principle Applied to the Foreign Exchange Markets, 1989