The counter つ (tsu) is the most useful counter in the Japanese language as it can be used for counting almost any object. Due to this propertly, it is sometimes referred to as a universal counter. In many cases it is perfectly acceptable to substitute the universal counter when we don’t know the counter to use for a particular object or thing. However, there are a handful of situations where the universal counters cannot be used. Some common examples include time, people, age, animals, floor, money, etc.