I am trying to find out why sheep has the plural sheep. I have found different explanations, such as, "it is because they were seen as uncountable, as in 'a herd of sheep'", "because it comes from German, which does not have the plural 's'" and that it is because it is a neutral Old English noun which does not change in the plural. Does anyone have the right explanation?
This is only my assumption or theory. In German it is das Schaf (singular neuter) and die Schafe (plural). But in dialects the final e is dropped and the plural is "die Schaf". I suppose that in the dialects of Old Saxon and other dialects of Anglo-Saxon this tendency was the same. I assume that especially farmers used this kind of plural (without -s) and this habit of speaking was adopted in the standard language. The plural without -s, i.e. singular and plural have the same form, is found with names of animals in the language of farmers, fishermen and hunters, people who use simple and often reduced language.
I can't prove this theory, but as the above posts show there is uncertainty and there are several explanations that are not very convincing. So I think it is justified to come up with another hypothesis which has some degree of plausibility.
Now, after writing this post, I've looked up what Grimm says in DWB. My view is not quite right, though I'm not far off. Grimm says the plural of the Old High German word for sheep has the same form as the singular. Later, in Middle High German a plural with -e comes up. So it seems that English has conserved the older system, plural without any ending, so that singular and plural have the same form.
Goose comes from an ancient Germanic word that underwent a process called "mutation" or "umlaut". When it was made plural, an /i/ or /j/ sound was added, causing the tongue to rise in preparation for making that sound, and changing the "oo" to "ee". Foot/feet and tooth/teeth show this same result. However, these changes took place thousands of years ago.
Moose is a Native American word, added to the word stock of the English language during the past four hundred years. By that time plurals were created in English simply by adding an -s or, in this case, when we are speaking of an animal used for food (deer/deer, sheep/sheep, fish/fish), no inflection at all in the plural.