Sure.

You can drag them over each other, or right click and 'create a new keyword within...'


When you search for mammal you will get your dog (and other mammals) and you boxer (and other dogs)

When you tag a pic of a boxer, it will be tagged dog and mammal.



Note that you can have duplicates (and might want them) so you can, in the dog example above) also have:
People>Professions>Sports>Boxer

So you can get a lot of information about your boxer dog by tagging it:
Mammal>Dog>Boxer

Hmmm, but in this case when you tag your dog as a boxer which set of tags would it inherit? Mammal or Sports Professions? Or both? Very handy if you have a boxing boxer.

I'll play with it to see how it works...

Also, you will get both dogs and sports people if you search only using 'boxer' (just like you do on Google hehehe). Oh, you will also get that nice car in your garage.

The answer is you have to use the correct tag. The easiest ways are to drag the tag onto the picture or drag the picture onto the tag. You know it is the correct one because it is in the list under dog.

You can also avoid duplicates, but this is one example where that is difficult.

I imported all mine but I have always organized my files as a "My Pictures" main folder on my hard drive with it broken down into general subject subfolders which are then broken into further defined sub-sub folders and sometimes even sub-sub-sub folders. All I did with LR4 was to tell it to import My Pictures and clicked on the button "include subfolders" that pops up in a window just before the import begins. When it imported, everything came in all at once and completely.

Be aware that LR4 only keeps track of what you have "imported" into it. If you add photos, folders, subfolders and such onto your hard drive (let's say from a memory card) using Windows Explorer or whatever Mac calls their file management, you have to tell LR4 to synchronize so it will review what's in the main folder it has already imported, look at your hard drive for a comparison, and recognize the new stuff to also import. Otherwise those photos will not show up in LR and you'll think they're lost but they aren't.

LR can directly import from the memory card when you plug it in, save them to hard drive, and skip the Windows Explorer step but I'm old school, new to LR, and still have geezer fear of doing it that way with very important work-related files. I'll work with it more with recreational fun family shots as I have time so I don't cause myself great damage if I lose something.

The one thing I fear a lot in LR4 is the "do you want to: Delete from Catalog or Delete from Drive" choice box. I am many times getting dozy at 3 a.m. while editing and could feasibly sometime click the wrong choice. I don't know yet if delete from drive is reversible in LR4 or not.