According to Russell, we should not forget that 'knowledge by acquaintance' sometimes deals with 'universals' and, 'knowledge by description' often expresses a linguistic description. Thus, according to him, there are two types of description. They are:

1. Indefinite description – a so and so
2. Definite description – the so and so

An indefinite description is a phrase of the form 'a so-and-so' and a definite description is a phrase of the form 'the so-and-so'. For him, a denoting phrase is a denoting phrase by virtue of its form; not by virtue of its denoting or not denoting a concrete object of this world. For example, even if there is no present king of France at present, 'the present king of France' is a denoting phrase (a definite description); 'a unicorn' is also a denoting phrase (an indefinite description) even if there exists no unicorn. Of course, ' the present president of India' and 'the student bearing roll no.-1 of this class' are, for example, denoting phrases (definite descriptions) which are denoting particular individuals in this world. But they are called denoting phrases solely because they confirm to the form 'the-so-and-so', not because they denote particular individuals.