Rule 8. With words that indicate portions—e.g., a lot, a majority, some, all—Rule 1 given earlier in this section is reversed, and we are guided by the noun after of. If the noun after of is singular, use a singular verb. If it is plural, use a plural verb.
Examples:
A lot of the pie has disappeared.
A lot of the pies have disappeared.
A third of the city is unemployed.
A third of the people are unemployed.
All of the pie is gone.
All of the pies are gone.
Some of the pie is missing.
Some of the pies are missing.
In recent years, the SAT testing service has considered none to be strictly singular. However, according to Merriam-Webster's Dictionary of English Usage: "Clearly none has been both singular and plural since Old English and still is. The notion that it is singular only is a myth of unknown origin that appears to have arisen in the 19th century. If in context it seems like a singular to you, use a singular verb; if it seems like a plural, use a plural verb. Both are acceptable beyond serious criticism." When none is clearly intended to mean "not one," it is followed by a singular verb.