The problem is that there are some words which don't look very English. Sometimes people forget whether they are singular or plural. One famous example is criterion which is a singular word, taking criteria as its plural.
The criterion for charter strength is
The criteria for distinguished club are
So you will see that criterion takes a singular verb because there is only one, but criteria takes a plural verb because there is more than one.
Of course, we can be more general than this, but simply put, one criterion requires a singular verb while several criteria requires a plural verb. Either of the following is correct.
Following the phenomenal success of this column, I have been asked to point out that exactly the same points as apply to criterionalso apply to phenomenon. If there's more than one of the things, then we're talking about phenomena. This probably applies to all words of Greek origin ending in -on. No doubt somebody can think of a counterexample.
While I'm still talking about plurals, let's look at a six-sided cube that has from one to six dots on each face. One of these creatures is a die and several of them are dice. You never have one dice*, just one die Why has this come about? I'm not sure but I think it dates from the ancestors of our politically correct brethren who presumably thought it an inappropriate word for parlour games. After all, they would say, we must "never say die", even when it is the correct word.
The District Grammarian admits defeat: animals with irregular plurals: I will fight for geese, sheep, deer and numerous other animal plurals, but I concede that kine are a lost cause. If you have one cow and add another cow, you now seem to have two cows rather than two kine. The language is moving on. Make a note that the plural of cow could be kine, however. It may come up in a trivia quiz some time.