Either A or B vs. A or B respectively

Question

In a comment on the Sustainable Living beta Stack Exchange site I wrote

The interesting part is the different transport mechanisms involved when it's either too cold or too hot inside.

Later on I was wondering if the either/or-construct would be the right one here.

Would it be better to say
"The interesting part is the different transport mechanisms involved when it's too cold or too hot inside, respectively"?

Right, context. It's about heat transfer, where the most relevant transport mechanism changes, depending on the heat going out (heat losses due to convection and conduction) or coming in (sun radiation).

Answer 1

"Respectively" is used to indicate two separate items being described in order:

In this picture the queen is holding a sceptre and wearing a crown to represent power and authority respectively

In this sentence, the word "respectively" means that the sentence is broken up into chunks thus:

In this picture:

1. The sceptre represents power.
2. The crown represents authority.

Respectively tells you that the list of nouns matches the list of descriptions 1-1 in the same order.

"Either" on the other hand represents a choice.

Would you like either fries or a salad with your meal, sir?

Here's a sentence that shows the two mixed together:

Would you prefer either the steak or the soup? They come with fries or bread respectively.

In this case "respectively" is used to indicate that the steak comes with fries, while the soup comes with bread. In particular, the steak doesn't come with bread, and the soup doesn't come with fries.

Answer 2

While Matt underlined the basic usage of "Respectively", let me add on usage of "Either": it underlines the options are mutually exclusive. In your example that's fairly obvious, but imagine this:

"Would you like mustard or ketchup with that?"
"Can I have both please?"
"Of course, here you are."

"You can have either an apple or a yoghurt with the meal."
"Can I have both please?"
"I'm sorry, but not within one set. You can buy either separately though."

In the first example you may choose first, second, both or neither. In the other the option "both" is unavailable, and later "either" is used as a synonym for "any of the two."

Of course using "or" without "either" doesn't always mean you can choose both, but using "either...or" invariably means limiting the options by making both unavailable.

There's also:

You must choose either left or right.

In this case, the option neither is removed too.