Learn Hardcore Chinese: tā hé tā shì péngyou.

他 tā (1st tone)
和 hé (2nd tone; see below on the rarer hàn)
她 tā (1st tone)
是 shì (4th tone)
朋友 péngyou (usually péng-yóu with a neutral second syllable in Mainland Mandarin; péngyǒu with a 3rd tone on yǒu is also heard)

No special tone sandhi occurs here.

Why do both 他 and 她 sound the same?

Mandarin doesn’t mark gender in pronunciation; both are tā. The female character 她 was created in the early 20th century to mirror “she” in Western languages. In speech, context tells you whether it’s “he” or “she”; in writing you distinguish with 他 vs 她.

How do listeners tell “he” vs “she” in speech if both are tā?

Rely on context and previous mentions.
Use explicit words: 男的/女的, 男生/女生, 先生/女士.
Use the person’s name.
Ask for clarification: 男的还是女的？
For “they”: 他们 (mixed/unknown gender) vs 她们 (all female).

Can I replace 和 with 跟 or 与? Are there differences? And is 和 ever pronounced hàn?

和 hé is the default “and” linking nouns/pronouns: 他和她是朋友.
跟 gēn is very common in speech and works here: 他跟她是朋友.
与 yǔ is formal/literary, mostly in writing: 他与她是朋友.
同 tóng is formal/older: 他同她是朋友.
Pronunciation: when 和 means “and,” standard is hé (2nd tone). A bookish reading hàn is sometimes heard in formal reading or set phrases, but everyday speech uses hé.

Can 和 mean “with,” as in “do something with someone”?

Yes:

他和她一起去: He goes with her.
我喜欢和朋友聊天: I like chatting with friends. 跟 works the same (often even more common) for “with.”

Why is 是 used here? Could I drop it?

是 is the copula used to equate with a noun phrase. Because 朋友 is a noun, you need 是: 他和她是朋友. Saying 他和她朋友 would be incorrect in this meaning. With adjectives, Mandarin typically does not use 是: 他们很好 (They are good). Using 是 before an adjective is possible for emphasis/contrast, but that’s advanced.

Do I need “a/the” like in English?

Chinese has no articles. 他和她是朋友 has no “a/the.” If you need “one (of),” use 一个, and for definiteness use demonstratives like 这/那:

他是她的一个朋友: He is one of her friends.
这是她的朋友: This is her friend.

Do I need a measure word like 个 before 朋友?

Not here. You add a measure word only when you quantify:

他是她的一个朋友: He is one of her friends.
他们是好朋友: They are good friends. (no number, so no measure word)

Is 朋友 singular or plural here? Why not 朋友们?

Chinese nouns don’t change for number. Here, 朋友 is effectively “friends” because the subject is plural. 朋友们 explicitly marks a group (often in addresses like 朋友们，大家好) and 他们是朋友们 is usually unnatural in this context.

How do I negate this sentence?

Use 不是:

他和她不是朋友: They are not friends. Pronunciation tip: 不是 is said bú shì (不 becomes 2nd tone before a 4th tone).

How do I make it a yes–no question?

Add 吗: 他和她是朋友吗？
Or use A‑not‑A: 他和她是不是朋友？ (shì‑bu‑shì) Typical answers: 是的/是 or 不是/不是的.

What’s the difference between 他和她是朋友 and 他是她的朋友?

他和她是朋友: He and she are friends with each other.
他是她的朋友: He is her friend (one‑sided statement; to make it explicitly mutual you’d also say 她是他的朋友).

Why not just say 他们是朋友? Does 他和她 add anything?

他们是朋友 = “they are friends,” with no detail about who “they” are. 他和她是朋友 explicitly names the two individuals (he and she). If you just want “the two of them,” use 他们俩.

How do I say “the two of them are friends”?

他们俩是朋友. (liǎ, 3rd tone)
他们两个是朋友. Casual northern style: 他俩是朋友.

Does 朋友 ever imply a romantic relationship?

No. 朋友 is platonic. For romantic partners, use:

男朋友: boyfriend
女朋友: girlfriend So 他和她是朋友 implies “just friends.” To say they’re a couple: 他们是男女朋友 or 他们在谈恋爱.

How do I talk about time or change of state with this sentence?

Add time words or aspect markers:

他们以前是朋友: They used to be friends.
他们现在是朋友: They are friends now.
他们成了朋友 / 他们成为朋友了: They became friends. (了 marks the change)
他们曾经是朋友: They were once friends.

Is the spacing in the example normal? How is it usually written?

Modern Chinese is written without spaces between words. The normal sentence is: 他和她是朋友。 The spaces you saw are a teaching aid.

What common mistakes should I avoid with this pattern?

Omitting 是 with a noun predicate: say 他和她是朋友, not 他和她朋友.
Adding 们 to 朋友 here: 他们是朋友 is correct; 他们是朋友们 is usually wrong.
Overusing 和 to link predicates: prefer 他又唱又跳 over 他唱和跳. (Note: linking verb‑object nouns like 唱歌和跳舞 is fine.)
Overusing 是 before simple adjectives: prefer 他们很好, not 他们是很好 (unless for emphasis).
Pronouncing 和 as hàn by default; use hé in everyday speech.
Mixing up 他/她/它/牠 in writing: 她 is for human females; 他 for males or gender‑neutral in speech; 它 for things/animals (牠 for animals is common in Taiwan).