Difference between “How do I ...” and “How can I ...”
For example:
How do I install this software?
How can I install this software?
Are they both right/appropriate?
Yes. They are both right, but may differ in meaning.
According to the Cambridge Grammar of the English Language:
- Will you go with them?
- *Want you to go with them? (* indicates that the sentence is ungrammatical.)
Thus auxiliary verbs can … invert with the subject to form interrogatives, but lexical verbs cannot. To correct 2 we need to insert the dummy (semantically empty) auxiliary do: Do you want to go with them?
In the given sentences we have what, for argument’s sake, we’ll say the ‘uninverted’ form is ‘[This is] how I install this software.’ Do is just the dummy auxiliary.
How is an adjunct that questions, among other things, manner, means and instrument.
- A: How did they perform? B: Extremely well. [manner]
- A: How did you manage to get in? B: By breaking the door open. [means]
- A: How are you supposed to eat it? B: With chopsticks. [instrument]
In this case, how is questioning the means of installation: ‘By what means do/can I install this software?’ (The question could also be one of instrument, i.e. ‘A: What do/can I install this software with? B: With this CD-ROM.’)
Having dealt briefly with do and how, I would say the first question could be rephrased ‘By what means do I install the software?’ to which the answer could be ‘You install the software by …’
Can is, as Neeth correctly pointed out, a modal verb. Can can express a range of different meanings, including ‘dynamic possibility’ (as listed in CGEL):
- What is reasonable or acceptable (You can always say you’re too busy.)
- What is circumstantially possible (Water can still get in.)
- Ability (She can run the marathon in under three hours.)
The questioner may be asking, ‘By what means is it reasonable/acceptable for me to install this software?’ or ‘By what means is it possible for me to install this software?’ or ‘By what means am I able to install this software?’ Context will give the actual question being asked. For example, a teacher might ask a class, ‘By what means is it possible for me to install this software?’ in order to get the students’ knowledge of all possible installation methods.
In summary, I would say in the first the questioner just wants to know how to install the software (maybe the easiest method, maybe the best method, maybe any method) but in the second, the questioner may want to know the reasonable/acceptable means, all the possible means or the means he is able to use (context will indicate which).
Of course, in informal English (especially in speech), there may be no distinction. If it’s in conversation, just tell the questioner how to install the software.
They both are right. How do I install would mean that you being sure of installing the software you require steps to install it.
In How can I install, 'can' is a modal verb. Here apart from the above meaning , it can also mean the different ways/possibilities in which you can install your software
Here do indicates that "I will install the software by determining the required steps" And "can" shows the lack of confidence to install the software.