Hi, Alexander!  Recently you wrote in a message to Ardith Hinton:   
      
   AH>  [re what cats are thinking]   
   ak>  The answer is of course that nobody knows.   
      
   AH>  On the surface of it, yes. Together with the British   
   AH>  & the Chinese, cats are said to be inscrutable...   
      
   ak>  When do we speak "cats" and when "the cats"?   
      
      
              My grammar texts are remarkably silent WRT the topic of articles.   
   Although a good English/English dictionary may be of some assistance, it may   
   have fewer examples than you'd like.  Hmm.  As long as everybody understands   
   the following is a work-in-progress, not a set of rules... [chuckle].   
      
      
              No doubt you're already more or less familiar with the use of the   
   definite article in examples such as...   
      
                        This is the cat   
                        That killed the rat   
                        That ate the malt   
                        That lay in the house that Jack built   
      
   ... a nursery rhyme which quite possibly dates back to 16th century England.   
   When we single out one cat (e.g.) from among many cats by describing it in a   
   unique way we use "the".  Although I could add some more recent examples, my   
   point would be that after 400+ years we still follow the same convention.  I   
   chose this example because it seems fairly straightforward & intuitive.  :-)   
      
      
      
   ak>  For instance, "The(?) cats are small animals."   
      
      
              Not all "cats" are small animals.  In the common parlance, "cats"   
   may = "felines" & include "big cats" such as leopards, lions, and tigers.   
      
              I think you're referring to the domestic feline (AKA felis catus)   
   ... to the exclusion of the latter... and you might have gotten away with it   
   if you hadn't mentioned size!  In generalizations such as this, however, the   
   singular may be used with "the" to refer to a particular genus &/or species:   
      
                        As a friend to the children   
                           commend me the Yak   
      
                                -- Hilaire Belloc (ca. 1926)   
      
   It seems to me that we often use "the" when we're categorizing in accordance   
   with a formal topic of study.  I do the same thing when I say "the comma" or   
   "the semicolon", but it is rather important to notice whether or not there's   
   more than one variety of [whatever].  I am not... nor have I ever claimed to   
   be... an expert in zoology.  But I know I can count on my GAGE CANADIAN & my   
   RANDOM HOUSE WEBSTER'S to offer just enough information about the scientific   
   names of various critters to reassure me that my usage of "the domestic cat"   
   (singular) & "the big cats" (plural) is thus far grammatically correct.  :-)   
      
      
      
   ak>  or "What do cats think when they look into a   
   ak>  washing machine?"   
      
      
              Yes, this version would be usual & appropriate in everyday speech   
   ... and now I can easily guess what sort of cat you are referring to because   
   it's unlikely you'd want to share your home with a Siberian tiger (or even a   
   somewhat smaller cougar or bobcat, for that matter).  Only domestic cats who   
   know where their next meal is coming from would IMHO remain fascinated by an   
   inanimate object such as a washing machine once they are quite sure it isn't   
   threatening to attack them & probably contains nothing worth eating....  ;-)   
      
      
      
   ak>  I am somehow not very sure (on the account of   
   ak>  the articles).   
      
      
              In short, if you make a generalization about "cats" without using   
   "the" I think you probably mean the variety people tend to keep as household   
   pets or barn animals & I imagine most others in the audience would too.  :-)   
      
      
      
      
   --- timEd/386 1.10.y2k+   
    * Origin: Wits' End, Vancouver CANADA (1:153/716)