Nope. Not crazy at all. My personal syle includes using my thumb in three different ways with multiple variations within those attacks. One is when I take the side of the thumb and strike the top fret like a hammer, two is the way more current players use in slap with the thumb (or in some cases double thumb strokes up and down) striking through the string off the fretboard, the third is more like a finger style guitar player (Flaminco to some) where the thumb is plucking very much in a finger style fashion. Double thumbing is in fact very much the technique you describe in your post. Beyond that I recommend the kitchen sink, any bottle neck you can get your hands on, an old violin bow...well just about anything can become useful if your willing to try.
I'd be curious to read more responses to this thread. I regularly use my thumb to strum/pluck my E string and my A string. I am self taught (so far) so I never gave much thought as to whether or not it was proper technique, it was comfortable.
After reading a few bass instruction books and all their definitive advice on how to play, I started stressing-out... No, don't use your thumb! You MUST alternate between the index and middle finger when plucking the strings. You must pluck with the index first, then the middle, wait, vice-versa. Aye-aye-aye! Then one night I was watching the Jimmy Kimmel show on late night TV and Sting was the musical guest. He came out and played a few of the old Police hits. I noticed that he used his thumb to fret the E string! That's when I said, "What the hell am I getting all stressed over what some book authors are telling us? Here is one of the premier bass players in the world using a technique that an instructor would hit you for!" Well, I still don't use my left hand thumb for fretting, but I have no problem using my right hand thumb for some shuffle riffs. Paul Mac
Yeah man. I use a pick mostly, but when it comes to reggea, I can only get the sound I want by playing only with my thumb 90% through the whole song and once or twice rake with my pointer and middle finger. I know it's illegal, but I just want some feed back from my fellow bass players. I have sinned.....
That's okay! Have you ever seen Richie Havens play "Here Comes The Sun" on a 6 string guitar? He tunes the open strings to a chord. Then he uses _only_ his thumb to press across the strings to sound another chord. Paul Mac
I use my thumb for chords, and for parts where there is lots of going back and forth between 2 strings w/ 1+ string in between them (like octaves) Kinda like for slap - like parts where slapping wouldn't be appropraite.