companion to four fingers?!

hrmmmm

What an understatement of a definition.
Thumbs are great...

• because their foot-counterparts, big toes, help us stand upright
• for holding chopsticks...and the other utensils, too.
• because they are so expressive. They are the only specific digits that can say "yea" and "nay" and "I feel pretty ambivalent about that." I guess they could even express halfway emotions, if you use the angles cleverly or something.
• because they are stout but proud. Even though they only have two segments, they don't have a complex or anything about it all.
• with kids. haha
• for hitchhiking purposes. You don't even have to have one of the hitchhiker variety.
• when you're painting your nails because of the relatively formidable surface area. What a relief to be able to start out on such a large palette.
• because it can be green. No one has a "green pinky."
• for playing the piano with extra force, or when you're trying to play octaves, or when you just feel like playing the piano with just thumbs.
• for opening doors and ovens like civilized people. 
• for holding pencils!
• to type with on a computer keyboard with expertise. Can you imagine how much longer/how much more effort it would take to move some other finger down to the space bar every single time you had to insert a space? ...I am tired just thinking about it.
• because it would be really hard to hold open stubborn paperbacks with just your four non-opposable digits. Dang.
• when you're picking out a piece of candy from the candy bowl

But you're right. There are some really important things that the other fingers do, too. Like pinky-wave at your friends and lovers, dip into sauces and soups to let you have a taste, pick nose holes (okay I guess you could pick your nose with your thumbs but...hmm), flick things off your blanket, wear the marriage ring on the marriage/love finger, press all the other keys of the computer keyboard and piano keyboard,  and close the clasps of necklaces/button buttons (yeah the thumbs need help a lot of times, but they're not ashamed of that). And other stuff. I guess it's the cooperation of all the fingers and their adjoint (is this even a word? Oh, oops.) friend the palm that makes up the whole magic of hands.

Yay for hands. Yay for thumbs. Yay for...all the fingers?! Oh no, generalizations wreak havoc once again.