Each OAuth-supported API provided by Hatena has "scopes", which describe permissions to kind of operations. This scope describes operation type of API. Developers need to specify which scope to ask a permission on a registration of an application or on requesting an OAuth access for a user. To know which scope you will need for a specific operation, please read the documentation for each API.. Note that a new scope may be added in the future.
Note: even user permitted write_private scope, it does not mean your application can also do read_public operations. (Again, read each API documents.)
read_public is required by an API which mainly reads public information.
write_public is required by an API which mainly reads, writes, modifies and deletes public information.
read_private is required by an API which mainly reads private information.
write_private is required by an API which mainly reads, writes, modifies and deletes private information.