Modals Are Mood Makers

Modal verbs do not describe actions. They describe attitudes toward actions. "I go" is a fact. "I could go" is a possibility. "I should go" is an obligation. "I would go" is a condition.

English modals never change form. No "cans," no "shoulds," no conjugation tables. They always pair with a bare infinitive — the verb without "to." You say "she can swim," not "she can to swim." This simplicity is a gift. Once you learn the meaning, the grammar is already handled.