When should one use 'who', and when 'whom'? A simple enough question on the face of it, but in practice a path through a quagmire.
Generally, making a choice between 'who' and 'whom' in constructs does not lead to a significant change in meaning. But it may. Consider the stock phrase "to whom it may concern." Here, the term 'concern' means 'be of interest'. By way of contrast, in the phrase "concern who it may", 'concern' may mean 'trouble', 'worry', or 'annoy'. Annoy who it may!
There are rules of grammar which people are fond of citing as proof that 'who' is correct in this sentence, and 'whom' is correct in that sentence. Rules? Correct? It is when people state that certain useages are in some way 'correct' that they demonstrate their own failure to treat linguistics as a science rather than a creed or dogma.
The laws of nations and the (prescriptive) rules of grammar have this in common: they are rules formulated for the specific purpose of controlling human behaviour. The difference between laws of nations and rules of grammar is this: the laws of nations have as their aim the control only of controllable human behaviour.
If a behaviour is automatic in all humans, the courts will not entertain any claim that such behaviour is in any way criminal. If someone holds me underwater, and in my struggles I kill them, I commit no offence in any civilised jurisdiction. By way of contrast, the pundits of pedantry would insist on their right to enforce on me their perception of the rules of grammar, without regard to my automatic use of the rules of fluency and euphony.
Bristol University would have me say "Whom did you see lurking around last night?" and "He would not tell me whom he saw in the shadows that fateful night." Tosh! Piffle! Tosh and piffle! Balderdash, even!
Whoever devised the test, linked to above, relies overmuch on the 'subject - object' model of sentence analysis. That model is based in Latin. It seems to be a little-known fact amongst grammarians and pedants that English is not Latin, is not directly or indirectly derived from Latin, has not absorbed Latin and did not model itself or its grammar on Latin.
To the average fluent speaker of English who has not been indoctrinated into the methods of the 'English must obey the rules of Latin' school of bull***, the 'object' of a sentence is its objective, its purpose, its raison d'etre or its point of focus. In any sentence mentioning a large number of fruit trees, the object of that sentence is an orchard!
In deciding between 'who' and 'whom', no reference need be made to 'subject' or 'object'. The rules of natural grammar are simpler. Here is an example of natural use of 'who' and 'whom' in a paragraph. It is taken from the presentation by John Quincy Adams to the Supreme Court in the Amistad case.
Who, then, are the tyrants and oppressors against whom our laws are invoked? Who are the innocent sufferers, for whom we are called upon to protect this ship against enemies and robbers? Certainly not Ruiz and Montes.I am confident that John Quincy Adams wrote that on the fly, from a natural love of natural language, rather than having looked up the 'correct' forms in a grammar book.
The natural language rules for choosing between 'who' and 'whom' are these:
Firstly, and exercising equally supreme powers are the rules of fluency and of euphony:
"If it doesn't sound right, it isn't right."
"If you have to stop to think about the grammar, the grammar is wrong."
There is only one rule of syntax:
When the word follows an expression of directed action, direction or location, use 'whom'.
When the word precedes an expression of directed action, direction or location, or such is not expressed, use 'who'.
Expressions of direction or location include prepositions such as 'in, on, for, towards, at' etc. Directed action is expressed by verbs such as 'hit, shoved, pushed', etc. "Who [verb phrase] whom?" Who killed whom? Who shall pay whom?
According to the second rule, it is 'grammatically correct' to say "At whom are you waving that gun?" But who would think to say such a thing? In a time of crisis, surely even the world's worst pedant would say: "Who are you waving that gun at?"
Pedants may keep their rules of Latin grammar. Pedantry isn't science.
The rules I give here for the determination of when to use 'who', and when 'whom' come from a welter of observations. It is observational science. It is linguistics.
Vivat the rules of natural grammar!
Concern who it may!