@ecovonrein wrote: ``Your "" does not satisfy ISBLANK. It just appears blank``
Right, and nothing can. (See below.)
But @jamesvinicombe did not specifically ask for that. On the contrary, he wrote: ``I have tried adding ,"" [...] and it does not work``. So I believe I correctly interpreted his question to be: how can we return "" (the null string)? And as you say, he seems satisfied with my interpretation.
As to your question.... The problem is: ISBLANK is a misnomer. It should be ISEMPTY. That is, in Excel, ISBLANK returns true only if there is no value (constant or formula result) in the cell -- which is the Excel definition of an empty cell.
And that is what the IS functions help page says about ISBLANK, to wit: ``Value refers to an empty cell.``
(Sadly, MSFT misuses the word "value" to mean either parameter or cell reference.)
But your confusion is understandable. Excel is imprecise and ambiguous in its use of the terms "empty" and "blank". For example, in the COUNTBLANK help page, the one-line description is ``count the number of empty cells in a range``. But a later remark in the help page states ``Cells with formulas that return "" [...] are also counted``.
(And once again, MSFT's choice of words is imprecise. COUNTBLANK counts any value that is the null string, whether it is a formula result or a constant. One way to create a constant null string is: enter the formula ="", then copy-and-paste-value back into the same cell.)
The bottom line is:
1. Use ISBLANK when you want to determine if a cell appears blank because it has no value.
2. Use A1="" when you want to determine if a cell appears blank because it has no value or its value is the null string.
3. Use AND(A1="",ISBLANK(A1)=FALSE) if you want to determine if a cell appears blank only because its value is the null string. (Very unusual, IMHO,)
And of course, use the null string "", not a string of spaces like " ", when you want a result that appears blank, because it is easier to use test #2 above, which is usually the intended condition, IMHO.
And as noted above, beware that a cell that appears to be empty because it has no formula might actually contain a constant null string. That can explain why A1+1 results in #VALUE, even though a (truly) empty cell is interpreted as zero in that context.
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Finally, IIRC, Google Sheets has a function that returns a truly "empty cell" result -- a contradiction of terms, IMHO. Thus, ISBLANK returns TRUE for that cell. If not Google Sheets, then perhaps Open Office. I don't recall, and I'm not taking the time double-check.
Also, I am not familiar with Office 365 Excel and all of its oh-so-many iterations and "beta" features. Perhaps a more-current version of Excel does or will have a similar function. I don't know.
