The two demonstratives are marked negatively for inherent number feature: [-Pl_Inh]. This means that the value of number is not inherent, but it must be assigned an absolute value--based on agreement.
These words belong to the class of function words called determiners, which serve to either identify nouns or word groups functioning as nouns or give additional information about them (the ...
PPT covers the role of determiners in writing, looking at articles, interrogatives, demonstratives, possessives and quantifiers. Examples are given for each and children asked to practise identifying ...