# What's a phrase for when: to do A, you first need to B, but to do B you first need to do C, etc? [duplicate]

Say you need to change a light bulb, but to do that you need to get a ladder, but to get the ladder you need to get into the tool shed, but to get into the tool shed you need to find the key, etc. This kind of quest where you are being presented a new task at each step before you can even start the previous one. I feel sure there's a phrase that represents this but I can't remember it.

Edit: I think I'm thinking of a story where an adventurer is seeking an object A, so they ask person 1, who is willing to give it but only if they receive object B. So the adventurer goes to person 2, who will only give up object B for object C, etc.

• One task is the "predecessor" (from Latin, steps before) of the next. At least, that's what we would say in Information Technology. You could also call it a "prerequisite" (needed before) for the next task. Look those up and see if one fits your need. If you want a fancy phrase, you could use "sine qua non" (that without which, not). Again, this applies to the task that must be done before the other one. The opposite of predecessor is successor. I don't know of an opposite for prerequisite or sine qua non. – Brian Hitchcock Feb 4 '15 at 3:54
• @Hellion That's similar, but I'm looking for a phrase, one that specifically talks about a large chain of these problems instead of just one. – tias42 Feb 4 '15 at 3:57

When one of the finite series of required steps requires that an earlier step in the series be performed first, the result is what Wikipedia calls a deadlock:

a deadlock is a situation in which two or more competing actions are each waiting for the other to finish, and thus neither ever does.

The idea is that you're faced not with an infinite number of turtles to climb, but with the same finite set of turtles over and over. So even though the number of specified steps isn't infinite, you'll never reach your goal.

Although a deadlock situation is especially familiar to computer users—and that is what the Wikipedia article focuses on—it can occur in bureaucracies (corporate or governmental) and other settings, too.

One classic presentation of a multistep deadlock is in the children's folk song "There's a Hole in My Bucket." In the song, Henry complains that his bucket has a hole in it, and his dear Liza explains what he should do to fix it—but each action she suggests raises another obstacle that needs to be overcome, until eventually she advises him to use a bucket to carry the water to wet the whetstone to sharpen the axe to cut the straw to mend the hole in the bucket. But...

There's a hole in my bucket, dear Liza, dear Liza...

Of such circular series of interlocking would-be actions are recursive deadlocks made.

• OP never hinted that the dependencies are circular. On the contrary, the chain is "long, but finite". – anemone Feb 4 '15 at 8:18
• @anemone: You're right—I jumped to that conclusion. I'll edit my answer to indicate that a circular situation is applicable to a finite series of contingencies only if one of the subsequent steps requires performance of one of the earlier steps. Thanks for pointing out the problem. – Sven Yargs Feb 4 '15 at 8:22
• There's a Hole in My Bucket is what I was thinking of, well done. It's not quite a phrase, so sorry for the misleading question. – tias42 Feb 4 '15 at 8:59

Infinite Regress is the Aristotelian phrase.

Turtles all the way down is a bit more fun.

• The one that I'm thinking of is long, but finite. See the edit I posted above. – tias42 Feb 4 '15 at 6:15
• @tias42 The infinite regress stops at the unmoved mover. – ben rudgers Feb 4 '15 at 12:34

first things first

Do things in the proper order; do not skip things that you should do first: http://idioms.thefreedictionary.com/first+things+first

It sounds like you're describing a chain of events, which Wikipedia defines with:

A chain of events is a number of actions and their effects that are contiguous and linked together.

A similar phrase is chain reaction, but in my experience that tends to imply that subsequent steps have less control over their reaction to their stimulus, as in a Domino Effect.

There may be a single word to describe these scenarios: This "Trading Quest" wiki entry for the Legend of Zelda video game series uses sequence to describe a situation similar to the one given:

The basic trading sequence [emphasis added] starts with Link acquiring an item, often by helping out another character. The item can then be traded to someone else who desires it, who then gives Link a new item to trade, and so on.

One rather technical term is "chain of dependencies", as in here. "Scheduling" is a keyword around which suitable terms might occur.

In computer science, topological sorting is applied to resolve scheduling problems.

Critical Path captures the shortest possible sequence of dependencies if parallel execution of tasks is allowed. A Gantt chart diagrams the dependencies and parallel execution paths.

Flow requirements also captures the idea.