Hi sir Joe,
How are you doing?
I've been very busy because of my new job that only today I got the chance to visit your forum, and while reading some of the new topics, this one caught my attention.
Allow me to answer this question.
The subject on her post is "Can an adjective be used as a subject in a sentence?"
I consider this as a tricky question.
Without analyzing the structure of the sentence and depending on who is being asked, one could get either a "yes" or a "no" answer.
In fact, there are some grammar books out there discussing "adjectives as a form of a subject", which for me is an oversimplification. (Correct me if I am wrong with my understanding sir Joe.)
Let us have some examples.
"The OLD and SICK are advised to evacuate the area."
"The RICH get richer, and the POOR become poorer."
"The INJURED were taken to the hospital."
By visual inspection, we can all agree that the form of the subjects in the given sentences above is an adjective.
IMAGE CREDIT: LEARNINGENGLISH.VOANEWS.COM This is what I meant when I said that the topic about adjectives used as a subject in a sentence is an oversimplification of the lesson. Why?
It is because some focus on the form and decontextualize the elements in the given sentences.
However, by carefully analyzing the sentences above and contextualizing the elements, we will find out that the subjects given above are an ellipsis of a noun phrase.
Probably, the complete form of the subject in the sentence "The OLD and SICK are advised to evacuate the area" is "The old and the sick RESIDENTS...", and for the "Rich become richer", the subject could be "The rich PEOPLE/POLITICIANS..."
And my answer to this question is a "no".
It's a "no" because the form of the subject is an elliptical construct of a noun phrase. Logically, the adjectives above are just a part of a noun phrase. Adjectives undergo nominalization, but it loses it categorical form. Once this happens, they become nouns.
Thanks, sir Joe