can

4. MODAL.

You use can to indicate that something is true sometimes or is true in some circumstances.

• long-term therapy that can last five years or more.    
• Exercising alone can be boring.     
• Coral can be yellow, blue, or green.

...Cobuild

2(c). Used to indicate probability or possibility under the specified circumstances: 

• They can hardly have intended to do that.
  

cf. 

2(a). Used to indicate possibility or probability: 

• I wonder if my long lost neighbor can still be alive. 
• Such things can and do happen.
  

2(b). Used to indicate that which is permitted, as by conscience or feelings: 

• One can hardly blame you for being upset.
  

... Am-Heritage