They do not learn the present participle and 3rd person singular present simple for regular or irregular verbs for another very simple reason - they never change. The present participle is always made by adding '-ing' to the base, and the 3rd person singular present simple is always made by adding 's' to the base (though there are some variations in spelling). Note that 'have', 'do' and 'be' also function as helping or auxiliary verbs, with exactly the same forms.
Example Sentences These example sentences use main verbs in different forms. Base - Infinitive • She helped him work on his homework. • We heard them sing their national anthem. • I want to have a drink.
• To be, or not to be, that is the question: Base - Imperative • Work well! • Have a nice day. Base - Present simple (except 3rd person singular) • I work in London.
• You sing well. • They have a lot of money. Base - After modal auxiliary verbs • I can work tomorrow. • You must sing louder. • They might do it. • You could be right. Past simple • I worked yesterday.
• She cut his hair last week. • They had a good time. • They were surprised, but I was not. Past participle • I have worked here for five years. • He needs a folder made of plastic. • It is done like this. • I have never been so happy.