One of our readers asked some time ago, “Why is someone who escapes called an “escapee”? Shouldn’t they be called an “escaper”? The prison, being the thing that is escaped from, should be the “escapee” I would’ve thought. Otherwise it implies that the prison has escaped from around the prisoner, rather than the prisoner from inside the prison. Does that make sense?”
In fact, it does from a linguistic point of view. To understand the relationship, you have to understand transitive and intransitive verbs. A transitive verb is one that has a direct object. In the sentence, “The man bit the dog, man is the subject and dog is the object. So, bite is a transitive verb.
In the sentence, “The man slept quietly,” Man is the subject but there is no object. In fact, the verb sleep allows no object: you can’t sleep something.
The suffix -ee is usually used to indicate the object of the underlying verb in noun derivations, so that an employee is someone who is employed, an inductee is someone who is inducted, a draftee is someone who is drafted. The suffix -er is usually used to mark the subject relationship. An employer is someone one who employs someone else, an inductor is someone who inducts other people, etc.
However, there is a strong tendency for English to use -ee to denote the subject of intransitive verbs (those that do not take direct objects), so that someone who stands is a standee “one who stands”, someone who retires is a retiree “one who retires”, someone who waits is a waitee. So it is not surprising that someone who escapes from confinement is an escapee, since you can’t escape something else but only FROM something.
If someone stands something else (in the corner, say), that person would not be a standee but a stander. A retiree must be someone who retires FROM something, not a person who retires things. To the extent a person can wait tables, that person must be a waiter. Notice that if you wait ON someone, you must be a waitee, since in this sense the verb requires a prepositional phrase with ON and does not allow a direct object.
The language isn’t entirely consistent in this (e.g. an attendee is someone who attends something) but the reason subjects of intransitive verbs are treated like objects of transitive ones, is that the subject of intransitive verbs functions semantically very much like the object of transitive verbs. For example, if you walk the dog (=object), the dog (=subject) walks. In the sentence, “I walk the dog,” with the transitive form of walk, dog is the object (the walkee). In the sentence, “The dog walks,” with the intransitive form of walk, dog is the subject even though he is doing the same thing in both instances.
So, while linguists are not sure quite why, the objects of transitive verbs are similar to the subjects of intransitive verbs and that is (sort of) reflected in the use of -er and -ee.