Episode 64: Einstein, Who Was Born in…

Non-defining relative clauses — Albert Einstein, 1955 (B1-B2)

Grammar Box

Meaning: Non-defining clauses add extra information that could be removed without changing the sentence’s core meaning. They’re like bonus details in parentheses, separated by commas.

Form: Use commas before and after the clause. Use “who” (never “that”) for people, “which” (never “that”) for things. The sentence works without the clause.

Example 1: “Einstein, who failed his university entrance exam the first time, became history’s most famous scientist.” (We already know who Einstein is.)

Example 2: “His theory of relativity, which revolutionized physics, was published in 1905.” (We’re adding information about a theory we already identified.)

Common mistake: Wrong: “My father who lives in Boston called yesterday.” Better: “My father, who lives in Boston, called yesterday.” (You have only one father, so add commas.)

The Challenge

Luna compared two sentences in her grammar book. “‘The scientist who discovered relativity’ versus ‘Einstein, who discovered relativity.’ Why does the second one have commas?” She frowned. “They both talk about the same person.”

The watch pulsed gently. Professor Wisdom appeared, adjusting his glasses. “Ah, the difference between identifying someone and adding information about someone we already know. Let me show you a biographer learning this lesson while interviewing the most famous scientist in history.”

The Journey

April 1955, Princeton, New Jersey. A young biographer named Abraham Pais sat in Einstein’s modest home office, where stacks of papers covered every surface and a violin rested in the corner. Einstein, who was 76 years old and had only days to live though neither man knew it, sat patiently answering questions for what would become one of the most important scientific biographies ever written.

Pais, who had been a theoretical physicist before becoming a historian, had prepared meticulously for this interview. He knew that Einstein, whose theories had transformed human understanding of space and time, rarely granted such extended access. The old man’s wild white hair, which had become almost as famous as his equations, caught the afternoon sunlight streaming through the window.

Einstein faced frustrations that few people understood. His unified field theory, which he had been developing for decades, remained incomplete despite thousands of hours of work. Younger physicists, who found quantum mechanics more promising, had largely abandoned his approach. The scientific community, which had once hung on his every word, now viewed his later work with polite skepticism rather than excitement.

Yet Pais noticed something remarkable. Einstein, who could have spent the interview defending his legacy, instead spoke with genuine curiosity about other scientists’ work. He discussed quantum theory, which he had helped create but later questioned, with respect despite his doubts. The old physicist, whose equations had once shaken the foundations of physics, seemed more interested in understanding than in being right.

As they talked, Einstein shared stories from his youth. He had been a rebellious student, which his teachers had found intolerable. His first marriage, which had ended in painful divorce, had cost him deeply. Patent office work, which most would consider boring, had given him the freedom to think without academic pressure. Each detail, which Pais carefully recorded, revealed a human being rather than just a legend.

The room smelled of pipe tobacco and old books, that distinctive scent which libraries and scholars’ studies share. You could hear the scratch of Pais’s pen on paper, the occasional traffic noise from Nassau Street which filtered through the window, the gentle creaking of Einstein’s chair as he gestured to emphasize a point. The afternoon light, which was turning golden as the sun descended, cast long shadows across mathematical equations that covered the desk.

The Deep Dive

Non-defining clauses add bonus information about something or someone we’ve already identified. They sit between commas like a side note. “My mother, who taught mathematics for 40 years, just retired” — we already know which person (my mother), so the clause adds extra detail. Remove it and the core meaning survives: “My mother just retired.”

The comma placement is critical. Defining clauses (no commas) identify which one: “Teachers who inspire students deserve respect” means only inspiring teachers, not all teachers. Non-defining clauses (with commas) add information: “My teacher, who inspires students, deserves respect” means we already know which teacher, and we’re adding that they happen to inspire students.

For people, use who in non-defining clauses, never “that.” “Einstein, that discovered relativity” is wrong; “Einstein, who discovered relativity” is correct. For things, use which, never “that”: “The theory, which changed physics” not “The theory, that changed physics.” In American English, “which” clauses almost always need commas; in British English, the rules are slightly more flexible but commas remain standard for truly non-essential information.

More Examples

History: “The Titanic, which was considered unsinkable, struck an iceberg on its maiden voyage and sank within hours.”

Science: “Penicillin, which Fleming discovered accidentally, has saved countless millions of lives since its introduction in the 1940s.”

Everyday: “My neighbor, who practices piano at midnight, finally bought headphones after numerous complaints from other residents.”

Formal: “The committee’s recommendation, which took six months to develop, was rejected by the board within minutes of presentation.”

Informal: “That restaurant downtown, which I’ve been telling you about for weeks, finally has an opening for Saturday night.”

Contrast: “Students who study succeed” (only those who study) vs. “These students, who study hard, will succeed” (all these students, plus extra info).

Practice & Reflection

Exercises:

Fill in the blank: “My grandmother, _____ is 90 years old, still walks three miles every morning.”
Correct the mistake: “Einstein that developed relativity was born in Germany.”
Choose and explain: Which is correct and why?
a) “My car which is blue needs repairs.”
b) “My car, which is blue, needs repairs.”
Rewrite: Add the information “She won a Nobel Prize” to this sentence using a non-defining clause: “Marie Curie discovered radium.”
Compare: Explain the difference: “My brother who lives in Tokyo” vs. “My brother, who lives in Tokyo.”
Your reflection: Write a sentence about your hometown using a non-defining clause to add interesting information.

Answer Key:
1. who — non-defining clause adding information (use commas)
2. Change “that” to “who” and add commas: “Einstein, who developed relativity, was…”
3. (b) — you have one car, so add commas for extra information
4. “Marie Curie, who won a Nobel Prize, discovered radium.” (adds information about Curie)
5. First suggests you have multiple brothers (identifying which one); second suggests one brother (adding where he lives)
6. Check: Do you have commas? Is the sentence complete without the clause?

The Lesson

Luna practiced writing in her notebook. “Albert Einstein, who changed physics forever, loved playing violin. I see — the commas show I’m adding extra information about someone we already know.”

“Precisely,” Professor Wisdom said. “Pais understood this instinctively. When you write ‘Einstein, who loved music,’ you’re not identifying which Einstein. Everyone knows who Einstein is. You’re adding a detail that makes him more human, more real.”

“So non-defining clauses are like… storytelling details?” Luna asked.

The Professor smiled. “Exactly. They’re the difference between a police report and a biography. ‘The suspect, who was wearing a red jacket, fled the scene’ — the jacket is extra detail. The core fact is ‘the suspect fled.’ Those commas create space for personality, context, and humanity in our sentences. Pais’s biography succeeded because he used grammar that added Einstein’s humanity to Einstein’s genius.”