Question: What is the difference between *to allege* and *to claim*? Can I use them interchangeably? Or perhaps I can only *allege* something illegal?

For example, from CNET:

> 
> Over the past several months, the two companies have been embroiled in
>  litigation in which Apple **alleges** that Samsung illegally copied
>  technology and design aspects of the iPad to create the Galaxy Tab.
> 
> 
> 

If I replace *alleges* with *claims*, does it change the meaning at all?

Answer: 
To *allege* is always to accuse a party (human or corporate) of wrongdoing. You may, however, *claim* something without the accusation of wrongdoing.

For example:

* You can *claim* that a new product is far superior to its competitors
* You can *claim* that a storm damaged your conservatory by blowing your neighbour's tree down so that it fell on the conservatory
* You can *claim* that the dog ate your homework

In none of these situations are you accusing anyone of anything (except, possibly, the dog. But he isn't a legally responsible entity and you aren't asking your teacher to take action against him).

You can *claim* that someone is guilty of wrongdoing against you but this can be less aggressive that *accusing* them of it. For example:

* You can *claim* that a rival's product breaches a patent you hold in some significant detail.
* You can *claim* that a neighbour's tree is damaging your conservatory because the branches are scratching the glass and wearing away the frame
* You can *claim* that your sister spilt coffee over your homework

If you *claim* negligence or deliberate wrongdoing on the part of another this is the same as *alleging* it:

* You can *claim* or *allege* that a rival has copied your patented product deliberately.
* You can *claim* or *allege* that your neighbour has cut down his tree so carelessly or incompetently that it has fallen on your conservatory
* You can *claim* or *allege* that the class bully has thrown your homework into the river.

There is an overlap in the meaning but *allege* is stronger, more associated with criminality and tends to imply a higher standard of proof. *Claim* is wider in application, slightly gentler and somewhat less formal in its implications.
Allege is used when no evidence is available so it is not sure or accurate yet. It is a statement that is made without giving proof, accusing somebody of doing something that is wrong or illegal.

Claim is used when evidence is available and it is sure and true.

the two words are not the same and cannot be used interchangeably.