A Puzzle, from My Friend Warren Usui:

Fill in the blank in the following list:

1. Vermont, Connecticut, New Hampshire

2. Pennsylvania, Delaware, New Jersey

3. Indiana, Ohio, Kentucky

4. Arkansas, Mississippi, Tennessee

5. Iowa, Missouri, Nebraska

6. California, Colorado, Arizona

7. Washington, ______________, Oregon

Dan Schmutter:
I believe the answer would be Columbia.

Dan Schmutter
11.12.2007 6:41pm
Waldo (mail):
11.12.2007 6:42pm
Dave M. (mail):

All the answers are states that share a common border on a river. Wikipedia has more.
11.12.2007 6:44pm
Dave M.:
Oh, Columbia is right. #6 contradicts my theory.
11.12.2007 6:47pm
WHOI Jacket:
Columbia, but too late to be thought of as clever.
11.12.2007 6:49pm
Puzzling Aside:
Under standard puzzle conventions, it seems that the puzzle has been solved by commenters above. As an aside, though, the desired answer, "Columbia," fails to satisfy another plausible condition: namely, that each line contains the names of three states. I wonder if we could ever get a computer to recognize these conventions.
11.12.2007 7:05pm
not as clever (mail):
umm...why "columbia"
11.12.2007 7:05pm
not as clever (mail):
ohhh....I see.
11.12.2007 7:06pm
Maniakes (mail):
Columbia may not be a state, but it is a Federal District and it does get electoral votes.
11.12.2007 7:25pm
abw (www):
Alright, someone kindly spell it out.
11.12.2007 7:50pm
WHOI Jacket:
The first and third places in the numbered rows are the names of states. The second is the name of the river that serves as a border between the two of them.

(ie. Pennsylvania and New Jersey are separated by the Delaware River, Vermont and New Hampshire by the Connecticut River, and so on and so forth)

This blog could stand for some /spoiler/ tags
11.12.2007 7:58pm
Dan Schmutter:
abw -

The middle name in each set is not a reference to the state of the same name but to the river which forms the border between the other two states.

The Columbia River flows along the border between Washington and Oregon.

11.12.2007 8:00pm
glangston (mail):
Well, I'll have to be content to claim I guessed correctly before I looked.
11.12.2007 8:06pm
Sasha Volokh (mail) (www):
WHOI Jacket: The entire comments section should automatically be considered /spoiler/ when a puzzle is involved.

Puzzling Aside: I think the failure of "Columbia" to (as in the other lines) be the name of a state is a feature, not a bug.
11.12.2007 11:11pm
If #4 had been Wisconsin, Mississippi, Minnesota, the jarring lack of geographical continuity might have made the answer a little more obvious to me.

Or maybe not.
11.13.2007 2:40am
Puzzling Aside:
Sasha: Agreed. It is a feature, not a bug. I merely wanted to point out that the puzzle solution is only unique given our background puzzle-solving conventions and is not unique absent those conventions.
11.13.2007 3:02am
Gordo, I had the EXACT same thought.
11.13.2007 8:04am
Gotta agree with Puzzling Aside.

The problem with puzzles like this is akin to: How many curves can be drawn between any given set of points? That is, and I leave this as an exercise for the reader, find a tripartite relationship that holds between the listed triples, then find a state to fill in the blank such that the relationship holds. Here's one: Do not border on Alaska. "But I didn't mean that!" Well, what did you mean?
11.13.2007 8:04am
Skyler (mail) (www):
Good puzzle, certainly got me. But I'm not going to whine about "spoilers" just because I didn't figure it out. I was going to say "Idaho."
11.13.2007 8:38am
Spartacus (www):
Has never been in my kitchen?
11.13.2007 12:06pm
jnet (mail):
11.13.2007 1:12pm