It's an understandable confusion, but it's also easily clarified by the concept of Causative Verbs.
Some verbs are actions that take place or exist in and of themselves -- or, better said, some verbs represent actions or states of being which a thing performs (more or less) alone.
A good example is "Fall"
I fall when I drink too much. Last week, I fell into a pool. I have never fallen into a pile of manure.
Those actions are performed by the subject and have no direct object. They are self-contained. The following, however...
I fell trees for a living. I felled three trees yesterday. I have never felled a redwood.
These actions are performed by the subject but have direct objects without which the sentences would probably not make sense.
I'm actually not a grammar expert, but I'd like to believe that I have a good, intuitive feel for rules and patterns, so let's apply that to "hang"
An apple hangs from that tree. Three apples hung from that tree yesterday. Pears have never hung from that tree.
No direct object needed up there. However:
They hang horse-thieves for their crimes. They hanged one yesterday. They have never hanged someone for jaywalking.
"hang" with a past tense "hanged" is a causative verb (just like "fell" with past tense "felled"), because this is a verb that causes an object to perform the action of its non-causative counterpart. Better said, "I hanged him" = "I caused him to hang" = "I did something and, as a result of that, he hung".
So, of course, a person can hang. We can say that "He hung by his toes", but, if we're focusing on the cause of his predicament, we must say "They hanged him by his toes."
But I say that an inanimate object demands the same grammatical treatment.
I hanged the laundry up last week, and it hung on the line for three days.
There is an interesting facet of the causative verb: Typically (and traditionally), it is a regular verb.
Hang-hung-hung is irregular, but hang-hanged-hanged is regular.
Fall-fell-fallen is irregular, but fell-felled-felled is regular. This same pattern applies to German. It may be the same in other Germanic languages, but I don't know. I also see that the system is somewhat broken in English. Take, for example:
Sit-sat-sat not causative ... and Set-sat-sat causative ... If I set something on the table, I cause it to sit.
Lie-lay-lain not causative ... and Lay-laid-laid causative ... If I lay my weapons down, I cause them to lie on the ground.
I say that the system is somewhat broken in that "set-sat-sat" and "lay-laid-laid" are not truly regular verbs. The latter is close, but the former is way off. Interesting, but not a surprise. English is full of inconsistencies. Anyway, "setted" would sound silly, and "lay-ed" went out of style with all those other "bless-ed" past tenses. If I were to reconstruct the words based on their German counterparts, I would write them so:
Sit-sat-set not causative ... and Set-setted-setted. causative
But enough of those verbs. There are some others that catch my eye. Whenever I notice that there are two (or more!) different possible past tenses for one verb, it makes me wonder... could this be evidence of a dying causative verb? Let's see what we can do... I don't put these forth as 100% certainties, but as my suspicions and musings.
The moon shines brightly tonight. But the sun shone more brightly. The sun has always shone more brightly than the moon. Not causative. No direct object required.
I shine my flashlight at the criminal. I shined it in his eyes to blind him. I have never shined a laser pointer at anyone. Causative. Direct object (flashlight, laser pointer) required.
I wake to the sound of birds every morning. I woke and heard thunder last night. I have never woken during a tornado.
I wake my kids for school every morning. I waked them earlier yesterday. I have never waked them in the middle of the night.
Now, that last one is a bit trickier, because there seem to be about a thousand different -- very similar -- verbs: Wake, awake, waken, awaken.. and past tenses: waked, awakened, awoke, wakened. I'll leave that one alone for now and bring attention to another one of interest to me:
plead-pled-pled or plead-pleaded-pleaded ? When the former, though long condemned as incorrect grammar, has been in use for hundreds of years alongside the latter, I have to wonder if there's not a legitimate reason? Could it not be that "pled" is the standard past tense of "plead", and that "pleaded" is the past tense of a causative form, a word meaning "to cause something to plead"? Perhaps when we "plead our case", we are causing our case to plead? If that is true, then we should have "pleaded our case", and our case should have "pled for understanding".
One last example -- and this one just for fun -- is visible in the word "methinks". There was, once upon a time, another word, "think", with a meaning similar to "appear" or "seem". This still exists on the fringes of antiquity in German, the word "dünken" (to seem) as opposed to the word "denken" (to think). If linguists are to be trusted, then "denken" (and think) are actually causative forms of this old-fashioned word "dünken" (the "think" in "methinks").
What we are saying, when we say "I think", is actually "I make seem", "I cause to seem", "I cause to appear". It is an active creation of an image / an idea in the mind.
What we are saying, when we say "methinks" (and what people still occasionally say in German with "mich dünkt") is "Seems to me..."
It is also worth noting that these two English verbs were, at some point, spelled differently. But, over time, their sounds had become so similar that their spellings followed suit and they merged into one word. Of course, it can't all make sense (God, I mean.. it's English) ... Think (and denken) are both irregular verbs. Think-thought-thought is very irregular. So, unless it turns out that people used to say "thinked", then the whole rule about causative verbs being regular can't be all that trustworthy.
For some strange reason, I find that fascinating.
So, one last thing. And this goes back to "hanged" and "hung". If an executioner hanged a man, and that man hung for two days, should we say that the man was hung or was hanged? Methinks (haha) many people answer that question based on whether or not an execution took place, and, though it could lead to the correct answer in that case, it could cause an error in another case. Behold the causative at work: Someone hanged a necklace around my neck. It hung from my neck for years. Was the necklace hanged by my mother? Or was the necklace hung by my mother? In my opinion, a passive "hanging" of this necklace and the aforementioned dead guy must be "was hanged". A man "was shot". Someone shot him. Maybe he shot himself, but, whatever the case, he was the target of a shooting. He had to have been the object of a sentence: "The robber shot him" or "He shot himself". There must have been able to have been a subject and an object to express that he was shot. It's quite tricky, so let's look at another one: "A hundred trees were felled" vs. "A hundred trees were fallen." In the latter sentence, we are describing the state of the trees with an adjective, "fallen". The trees fell (somehow). Now they are fallen trees. In the former sentence, we are reporting what happened. Someone felled them. They were felled. Now they are felled trees.
So what are we describing? The state that something is in? ... or the forces which acted upon that something?
Also, in active sentences, since a causative verb MUST have an object, and a non-causative verb often MAY NOT have an object, could it be so different in passive sentences?
Let's take passive sentences and transform them into active sentences, because I'm just as uncertain as I hope you are.
"The man was shot by the robber." ..... "The robber shot the man." Easy.
"The tree was felled by the lumberjack" ..... "The lumberjack felled the tree." Easy.
"The tree was fallen." .... huh? Wait. By what? There can be no causative agent. "The tree was fallen by...." No. It doesn't work. This is not a passive sentence. It is a simple description using an adjective.
For redundancy's sake, let's try it a different way.
"The man was shot". .... "Who shot the man?"
"The tree was felled" ... "Who felled the tree?"
"The tree was fallen" ... "Who .. uh ... made the tree fall?"
If you can think of a better active sentence for the fallen tree, please comment. Now, however, I'd like to apply this to the "hanging".
"The man was shot by the robber" .... "The robber shot the man."
"The man was hanged by the sheriff" .... "The sheriff hanged the man."
"The man was hung by the sheriff" .... "The sheriff hung the man."
Can that last example be correct? In my understanding of "hung/hanged", no.
"The man was shot" ... "Who shot the man?"
"The man was hanged" ... "Who hanged the man?"
"The man was hung" ... "Who hung the man?"
Blegh. No way.
For the sake of switching things up, let's try this.
"The man died"
"The tree fell"
"The tree felled"
Obviously, that last one is nonsense. So how about this?
"The man died"
"The thief hung"
"The thief hanged".
Again, that last one? It just doesn't work. The person who "hung" is the one being killed. The person who "hanged" is the one doing the killing.
I think I've repeated myself enough, now. Soooo... if you read this to the end, you ought to be rewarded for your patience!
Well, tough luck.