It is natural to wonder what the difference in meaning is between the compound and non-compound forms of a given verb in contexts where either form occurs. There is no formula that can be mechanically used to decide when to use a compound verb and when no to. Not enough is known about the meanings of the compound verb to provide such instruction, even if there were space to write it all down. Correct use of the compound verb is a matter that is much more complex and subtle than learning the correct use of the causative or the subjunctive. It is something one learns gradually over the years, after hearing and seeing the compound verb thousands of times and after making many mistakes which , with a bit of luck, native speakers of Hindi will correct. However, this is not to make an unfathomable mystery out of it. There is a great deal one can learn by conscious attention, study, and practice.
     First we will look at some general formulations of the difference in meaning between the compound and the simple verb. Then we will examine how these differences are realized in concrete situations.
     An action may be thought of as consisting of a number of stages or phases. First is the stage of inaction, of intention and preparation; then comes the stage of effort; then the consummation of action leading to achievement, change or transition to something new. In most general terms, using a compound verb allows the mind to travel across the phases of an action. Using the simple verb illuminates a single stage. (However, the choice of when to let the mind travel fully through the phases of an action and when not to is not a matter of simple whim. There is remarkable agreement about when a full look is appropriate and when a simple flash will do. This agreement is such that speakers of Hindi are able to restore an author's choices to a doctored text with a high degree of accuracy, provided they are able to see the full context.)
     If someone says   ev:#ant: km:rð m:ðø Aay:a in one's mind's eye one sees Vikrant inside the room. But if one says   ev:#ant: km:rð m:ðø Aa g:y:a , this fairly simple picture becomes complicated or deepened in some way. One may think of Vikrant as someone successively outside and then inside the room. One becomes conscious of both the process and the result of Vikrant's passage into the room. Or, depending on context or intonation, one may come to know the speaker's attitude toward this event, that is, how it changed him. Perhaps he was anxiously waiting for Vikrant and was relieved by his arrival. Or perhaps he was quite happy before Vikrant came and annoyed him by his entrance.
     Using the non-compound to express an action usually indicates that the speaker is interested only in registering the result of the action. That is why the simple verb occurs to express actions whose results are routine, predictable or at least not out of the normal:

   1.  Aaj: s:Øb:h m:ØJ:ð Aap:ka 18 n:v:mb:r ka Q:t: em:l:a .
        'I got your letter of November 18 this morning. '

To say   em:l: g:y:a here might imply that I was unhappy to get it, or that I had been anxiously waiting for it or that it had been lost and I found it again. The compound verb supports numerous possible interpretations. Another example:

   2.  m:ðra j:n:m: uÀis: s:aò b:y:al:is: m:ðø hØAa.
        'I was born in 1942.'

To use the compound   hað g:y:a here would have humorous effect: I was born by mistake or without wanting to or after having waited around (in heaven?) for a long time. Or after several attempts. In short, using the compound instead of the non-compound forces the hearer to entertain one or another implausible alternative to my simply being born when I was.
     Sometimes a non-compound is used not to record a result without attention to the activity preceding it, but to record preceding activity without attention to the result. The non-compound  t:s:v:ir b:n:at:a hÜú in (3) refers to the effort to form a mental picture, but in itself does not imply a successful completion of that effort:

   3.  m:òø t:s:v:ir b:n:at:a hÜú l:ðekn: t:s:v:ir n:hiø b:n:t:i.   (film song)
        'I try to form a picture but the picture doesn't form.'

Substituting the corresponding compound form  b:n:a l:ðt:a hÜú for  b:n:at:a hÜú in the context of (3) creates a contradiction.

      While completeness is one of the primary meanings of the compound verb, it is not its only meaning. In each of the following sentences taken from Premchand's  g:aðdan:  the action is the same action and the subject (a bird) is the same, too.  There is no difference in completeness: