Why is countif showing 2 for an array list

hi labogola. not sure what you mean when you say if you don't use arrays, it'll return one. it doesn't have any relevance here if you simply look at it as a single value. it is meant to return an array of results for the formula to work. since List refers to A2:A20, doing COUNTIF(List,List) is as though you're doing:
=COUNTIF(List,A2)
=COUNTIF(List,A3)
=COUNTIF(List,A4)
and so on until A20. so since the above results give you 2,1,1 & so on, the COUNTIF(List,List) all 19 results:
{2;1;1;2;1;1;2;2;1;2;2;2;1;1;1;2;1;1;1}
you can get that by selecting the formula portion & press F9 to calculate.

the purpose of the above is to be continued with a logical test to see if they appeared more than once. so COUNTIF(List,List)<>1. since you only asked this portion, i suppose you're ok with the rest of the formulas

Hi,

"I don't get then what =countif(list,list) is doing if it's only returning 1 in a cell, and if I do it in a few cells it'll just return 1,1,0,0..0..0 etc..."

Not sure what you mean here - are you trying to enter =COUNTIF(List,List) into single cells?

When coerced to an array, COUNTIF(List,List) will produce e.g. {2;1;1;2;1;1;2;2;1;2;2;2;1;1;1;2;1;1;1}. However, that is not to say that this array will be returned from a stand-alone formula such as =COUNTIF(List,List).

And, even when array-entered, you will not be able to 'see' the entire array contents in one cell: you would need to select as many cells as are elements in the array before committing the formula in order to see the individual elements in separate cells (or press F9 in the formula bar, though this is not quite the same thing).

Regards