What noun can be both countable and uncountable?

Answer 1

Nouns for substances are uncountable nouns, the plural forms are reserved for 'kinds of' or 'types of'; for example:

• some tea, a cup of tea, a pot of tea, a pound of tea; or a selection of teas including black, green, white, or oolong.
• a bag of flour, a pound of flour, a cup of flour, a dusting of flour; or some flours are wheat, corn, rye, and oat.
• a cake of soap, a bar of soap, a box of soap, flakes of soap; or soaps such as jasmine, lavender, rose, aloe, and lanolin.
• a board of wood, a slat of wood, a length of wood, a piece of wood; or woods such as oak, pine, ash, maple, and mahogany.
• glass is the tricky one: glass is a singular uncountable noun for a pane of glass the plural form is two panes of glass; glasses is a singular uncountable noun for a pair of glasses, the plural form is two pairs of glasses. However, the noun glass used for beverages is a count noun; a glass of juice or two glasses of juice.