The inumber is a unique ID for the file. A file might be accessible by a number of different names through links. Therefore, the pathname does not uniquely identify a certain file. The inode for a file contains a field that counts the number of references to the inode. Note that only hard links to a file contribute to the reference count.
Hard links refer directly to the inode for a file.
Soft links just contain a pathname. Resolving a hard link to an inode is a one-step process, while resolving a soft link may need multiple steps that have to traverse the directory hierarchy. Also, soft links do not contribute to the reference count of an inode. Symbolic links also allow links to directories. Suppose a page is copied from one process P1 to another process P2.