I recently started a band that plays a mixture of blues, rock, and funk. I am the only one in the trio that knows any music theory. Can someone tell me how to explain to my band members that they should learn theory also? Or why I should not worry about it
I've had various bands with members who know differing amounts of theory. Some people knew no theory and others had degrees in music. In the long run, it usually made no difference as those who really knew no theory had a good practical of things. Those who knew the theory could learn songs much faster. In one band, I was able to help by going through fake books and learning songs that we had never heard. Those who knew theory could play songs heard on the radio (cassette tapes were the most advanced in those days) rather quickly. We could hear a song on Wednesday, practice in the garage on Thursday, then play that song for dances on Friday and Saturday.
In practice, a good knowledge of theory (whether from courses on just picked up) made things go faster. One need not have the expertise to play a lead in four-part counterpoint to contribute, but an ability to transpose on the fly is important. (As is the ability to have a visiting artist show up, play a song, and play a full backup with leads on songs never heard before. Real time learning.)
I'll focus mainly on the
Or why I should not worry about it
part of your question.
I believe that in bands, the most important thing is to be able to play the songs you want (and compose if you like). I recently played with a pianist that didn't know anything about theory, but could work out pretty much everything with his ear. I don't think I would go to that person and ask him to learn music theory. I mean, for a band he can do really good.
I've played with other musicians that didn't know much about theory, but could work out songs with their ears and the only problem I have had with them was the communication part. Let's say we want to work on a chord progression like vi-ii--V/V-V-I. When a person knows theory, he can easily understand what I just said; but some bandmates that don't, will have to have some time to understand. You might have to play the progression for them to hear and/or explain what notes are being played, which will be a bummer and will take time off your rehearsal time.
So what I will suggest to you is to see how much time you lose at the first few rehearsals to stuff like these; stuff that could be easily explained if everyone there knew theory. If you see that everyone gets on without any trouble and there is no time loss, I don't think there is much need for them to learn music theory. Otherwise, I'd suggest you talked to them, say the facts, like the time loss in rehearsals etc, and say that it'd be good for them to learn music theory, so that you all can communicate and develop faster. I believe that you can try to teach them yourself the very basics of theory, which will be helpful to them if you are friends.
If you are too forceful of the issue, your band members may not take it too kindly. If they are fairly accomplished musicians and are interested, they would have probably looked into learning theory already. Perhaps you could wait until a situation in the band comes along where theory has proved itself useful and tell them then. There are some musicians who take the opinion that theory is a bad thing and it'll cause them to lose their soul. In a case like this, it probably isn't worth making any effort to persuade them otherwise.
If your band is just learning and playing cover songs note-for-note, then having theory knowledge may not be as important. However, if you are writing your own songs or doing any improvising then music theory will certainly be beneficial.
Music theory is a very broad topic and there are so many aspects of theory that can be extremely useful. Verbally communicating ideas has already been covered in other answers but I'll add a few more examples of how theory could be useful to your band. Knowing scales will help when composing/improvising instrumental solos and vocal melodies. Knowing chord structure and keys will help with creating interesting chord progressions and vocal harmonies. Knowing chord inversions will help the bass player come up with interesting bass lines. Knowing rhythm theory like subdivisions, polyrhythms, etc. will help with creating interesting rhythmic patterns for the various instruments and having them all work together. The sky is the limit with how far you want to take it.
Can you create songs by ear without any theory? Absolutely! But knowing theory will undoubtedly help you in that process and might give you new ideas that you would not come across just tinkering about by ear. It also might help you understand why certain things sound particularly good. Music theory is simply a variety of tools which can help you to better understand music and be creative. It is definitely worth taking some time to fill your toolbox.
In the band I was in most recently, the two members who had the best traditional music theory knowledge were actually the worst at working out songs by ear; sometimes it even seemed that their presuppositions misled them into thinking that a song 'should be' one way, when in fact it was another. (Of course, correctly understood, knowledge shouldn't 'hurt' like this, but correct understanding can take time!)
Rather than making the blanket statement that "learning theory makes things go faster" (which will be true in some situations, less so in others), I'd suggest you identify the particular places where there is a theory 'tool' you can use, and just use it - if you're right, the benefit should be obvious to all band members without any persuasion being necessary.
Even though your band is playing modern styles that don't require "technical" theory as would be required for, say, classical music, having a knowledge of "how music works" is still important to successful playing in those genres. For example, your drummer is going to drum more confidently if he understands how the rhythms of the piece fit together; your rhythm guitarist is going to have an easier time learning the chord progressions if he understands why those chord progressions are used; your pianist is going to improvise nicer fillers if he understands the chords in the piece, knows what intervals and notes make up those chords, and knows what notes will sound good over the top of those chords (and can do all of this as he is playing). (Obviously I don't know what your exact line-up is, but you get the idea.)
In short, a solid knowledge and understanding of certain areas of music theory is important to confident and interesting performance, even in modern styles of music.