Emphasis with 是

You already know 是 as the verb "to be" (我是学生). But 是 has another important function: it can emphasize or affirm the truth of a statement, much like English "do/does" for emphasis. "I DO understand" = 我是懂的.

This emphatic 是 typically appears before the main verb or adjective: 他的成绩是不错 — "His grades ARE pretty good" (confirming, perhaps against doubt). 我是想帮你，可是没有办法 — "I DO want to help you, but there's no way." The emphasis often responds to an implied question or doubt.

In this pattern, 是 is usually stressed in speech. It often pairs with 的 at the end (making it similar to the 是...的 construction), but here the focus is on confirming truth rather than highlighting a detail: 这件事我是知道的 — "I DO know about this matter."

This usage is common in conversation when you want to concede a point, correct a misunderstanding, or insist on something: 你说得是有道理 — "What you said DOES make sense." 我是去过北京 — "I HAVE been to Beijing (despite what you think)." Learning this usage will help you understand nuances that textbooks often skip.