Grueber said:
why would perpendicular fail? Please give an example where something could only be played using the parralel method
Honestly, you guys really need to read a little more carefully.

It said nothing about perpendicular style failing... (this is exhausting).
I was speaking from the perspective of an educator. Students need clear procedures and a good model/example from which to learn. If I don't provide these, then I am setting my students up for failure.
I have an entire post that speaks to teaching slap bass in a certain way. I am not going to teach my students to play with their thumb pointing down. They can do that on their own if they want to. They might come up with some really cool things, but I am going to teach them parallel to the string.
This thread has been a little exhausting for me. I feel that I'm repeating some things over and over in defense of things that I'm doing with my students. I also feel that some of the things I'm saying and sharing are getting read out of context (the reason for this post).
I also feel that readers/posters of this thread are looking for opportunities to pounce on any statement that looks contrary to what they think or practice. That's fine. It's an open forum and people get to read the posts and make their own decisions.
I tried to be helpful by posting links to slap lessons from pro-bassists. These guys are amazing musicians: Bunny Brunel & Michael Dimin. IMO; if you want to be highly successful, then you study the work of successful people. I know that this statement is going to bring examples of people that slap with their thumb down, and that's great.
It might be a little more productive if we offer each other examples of excellent musicians rather than debate the direction of the thumb. Then, we can make our own informed decisions. But as for me and my students, we will slap parallel to the string.
I sincerely hope that I did not hurt any feelings in this post.
Joe