Is "Four times more" grammatically correct? And, if so, what precisely does it mean?

I have 10 beans. Jim has four times more.

Is this a valid sentence? And, if so, does it mean Jim has 40 or 50 beans?

Solution 1:

I would recommend against using four times more in this context, although it would generally be understood to mean 40. What I would say is four times as many.

Googling four times more and four times as many, it seems that four times more is generally used with uncountable nouns, and four times as many with countable nouns.

four times more cancer-causing tar.
four times more carbon emissions.

versus

four times as many journalists
four times as many males.
four times as many films.

I won't do more than mention the confusing construction four times as many more, which I would recommend against using, as I think it's ambiguous.

UPDATE:

The grammatical rule is: use X times as many with countable nouns, and X times as much with uncountable nouns. The construction X times more is grammatical with both, but as many and as much are clearer in this context. Modifying adjectives, however, you should use four times more (or four times as):

four times more likely.
four times more prevalent.
four times more dangerous.
four times more effective.

Solution 2:

I think the sentence makes sense to the question how many beans do you have and how many does Jim have.

You have 10 and Jim has four times more.

From a "scientific" perspective, the more than/ as many part of the expression indicates "direction"— think vector, rather than scalar. "More" indicates who has the greater quantity. The "four times" indicates the degree of the comparison — you have four times fewer than Jim. The more/as many and few/less than are analagous to "multiplied by" or "divided by" in mathematics.

Then, as the comments above point out, the correct form to use depends on whether the noun is countable or not.