Learn English – A does the same B as does C

In normal English syntax, single-word modifiers precede the noun they modify, but phrases follow the noun.

So you put the -ing word before the noun it modifies when it is acting as an adjective, not as a non-finite verb. You put the -ing word after the noun when it is part of a verbal phrase with other parts in it; you can’t have a long verbal phrase preceding the noun it modifies.

Sometimes the -ing word is actually a noun: a writing desk is a desk for writing, not a desk that happens to be writing. But it is still modifying desk. Here are examples of the -ing word used as a modifier (either as adjective or a noun) preceding the modified noun:

answering machine, barking mad, bleeding heart, bowling alley, burning bush, burrowing owl, carrying capacity, changing room, chattering classes, closing credits, coloring book, cooking oil, creeping thyme, dictating machine, drawing board, drilling rig, eating disorder, fighting drunk, firing squad, floating bridge, flying fish, flying buttress, flying fox, flying fuck, growing pains, heating element, holding pen, hopping mad, killing field, landing gear, laughing gas, lending library, lightning bug, magnifying glass, mailing list, missing person, moving walkway, opening night, parking meter, plunging neckline, praying mantis, quaking aspen, revolving door, rising sun, rounding error, scalding hot, shifting use, shouting match, starting line, talking point, thinking cap, trading post, waiting game

On the other hand, here are pairs of examples where the first one has the -ing word first where it acts as a simple adjectival modifer, and where the second one has it acting as an actual verb:

• the acting director had harsh words for us
• the director acting in the company’s best interests keeps a tight ship
  
  
• the binding action of this substance
• the cord binding the two halves together
  
  
• the bouncing ball hit me in the face
• the ball bouncing down the stairs was lost forever
  
  
• the calling function retains its own private variables
• the woman calling for a new husband will soon enough find one
  
  
• the carrying case was very heavy
• the case carrying the lead was heaviest of all
  
  
• the circling vultures drifted ever higher
• the vultures circling above our heads would wait until we dropped
  
  
• the cooking sausages smelled fabulous
• the women cooking our breakfast made us wash up first
  
  
• a demanding teacher is hard on the students
• a teacher demanding full attendance is seldom listened to
  
  
• the facing audience recoiled
• the man facing the audience cheered

And so on and so forth. In your case, you could have put sleeping afterwards, and had a man sleeping under the tree, but sleeping men like sleeping dogs are not particularly unusual.

However, you would not normally speak of fishing men, so you would have a man (who was/is) fishing for something down by the river bank. If you strained it, you could build up a context in which fishing men might contrast with farming men or some such, but it would be abnormal.

You might find a man singing in the rain, or you might find a singing man (who is out) in the rain, but you will never find a singing-in-the-rain man. Or to put it more crudely, there is a world of difference between having a fucking idiot in your livingroom and having an idiot fucking in your livingroom.

You mustn't believe all you read, especially about grammar. Why do people sometimes say that "be" can be either an auxiliary or a "lexical" verb? I don't know what "lexical" is supposed to mean here, but that's what they say. But why?

Well, here's my theory. "Auxiliary" in this context means "helping verb", and sometimes there is a following verb that you can imagine that "be" helps, like the present participle of a verb in the progressive aspect. But sometimes there is no following verb for the "be" to help, in which case it can't be an auxiliary and so it must be a "lexical" verb itself (since as we all know, every complete declarative sentence must have a verb).

Does that make sense? Alas, no, because it's not based on any facts of language, but instead, solely on terminology. Maybe we call the "be" that goes with an accompanying verb an "auxiliary verb", but that doesn't prove anything about that "be". Maybe "auxiliary" is an appropriate term, but maybe it isn't.

I could declare that all nouns beginning with the letter "k" are a special part of speech called "kymniad". Would you believe me?

According to the only syntactic tests I know of for what is an auxiliary, the "be" that accompanies another verb works just like the "be" that doesn't. For instance, auxiliaries are inverted in order with a sentence subject in questions, unlike ordinary non-auxiliary verbs:

You are eating. -- Are you eating?
You were seen. -- Were you seen?

Ordinary verbs don't work this way in contemporary English:

You eat halibut. -- *Eat you halibut?

So, we might expect the "lexical" verb "be' to work like the ordinary verb "eat", right? But it doesn't -- not at all.

Are you a halibut? (not *Do you be a halibut?)
Are you in the kitchen? (not *Do you be in the kitchen?)
Are you purple? (not *Do you be purple?)

So where is the language evidence that there is a grammatical difference between "auxiliary be" and "lexical be"? Nowhere.