Latest / The Copywriting Podcast with Fexingo: Sales Letters, Headlines, and Persuasive Writing / How One Underlined Phrase Lifted Response by 87 Percent
Transcript
- Lucas: So here's a number that keeps me up at night — eighty-seven percent. That's the lift in response Gary Bencivenga got from one single underlined phrase in a direct-mail letter for Boardroom Inc. back in 1984. Luna: Eighty-seven percent from an underline? Not a new headline, not a different offer — just drawing a line under some words? Lucas: Exactly. The letter was for a financial newsletter — I think it was Bottom Line / Personal. The control version had the benefit statement in bold. Bencivenga changed exactly one element: he took that same sentence and underlined it instead. Same wording, same position on the page. Underline beat bold by eighty-seven percent on response rate, and the revenue difference was even wider — three point two times the control. Luna: That's absurd. Why would an underline perform so much better than bold? They're both just emphasis. Lucas: Right, and that's the puzzle. The psychology explanation is something called processing fluency. Our brains are wired to read underlining as a signal that something is a link or a destination — it implies the reader should pause and pay attention. Bold, on the other hand, just says 'this is important,' which is more abstract. The underline is mechanical: it literally points to the words. Luna: So it's almost like a physical cue — like a finger pointing at the line. Lucas: Exactly. And Bencivenga tested this across multiple mailings. In one case, the underlined version pulled a three-point-two-to-one revenue multiple over the bold version. That's not a fluke. The copywriting community has known about this for decades, but it's surprisingly rare to see it used deliberately. Luna: You know, it's funny — if these marketing conversations have sparked something you've actually used, a couple of dollars a month is genuinely what keeps this show ad-free and going. It's at buy me a coffee dot com slash fexingo. No pressure at all, but it makes a real difference. Lucas: Yeah, absolutely. And we're grateful for every single supporter. Now, back to that underline — let's talk about why it works neurologically. Luna: There's actually a study from 2004 by psychologists at the University of Michigan — they found that underlined text is processed more quickly than bold or italic text. The brain's visual cortex treats the underline as a spatial anchor, so the reader's eye lands on the phrase faster and with less effort. Lucas: That's the processing fluency theory in practice. The easier something is to process, the more positively we evaluate it. So an underline doesn't just draw attention — it makes the message feel truer, more credible. Bencivenga didn't know the neuroscience, but he had the data. Luna: So what's the modern equivalent? In digital copy, underlining usually means a hyperlink. Do we lose that effect because people associate underlines with clickable links? Lucas: It's a risk. But you can still use underlining in contexts where the reader doesn't expect a link — like in a subject line, or in a headline on a landing page where the underline isn't blue. The key is contrast. If everything is underlined, nothing is. But if you underline one key phrase in a headline, it still works. Luna: I've seen some tests where underlined call to action buttons outperformed non-underlined ones by about fifteen percent. But the underline was on the button label, not the button itself. Lucas: Right, and that's a smart application. The button label 'Get Started' with an underline under 'Started' — it's a micro-cue. But I think the real power is in longer copy, like a sales letter or an email. One underline per piece, maximum. Bencivenga only underlined one phrase in that entire letter. Luna: What was the phrase? Do we know exactly? Lucas: The record says it was 'the safest way to earn twelve percent' — the underline was under 'safest way.' That's the benefit: safety and yield combined. The underline made the reader stop and think 'wait, how can it be safe and twelve percent?' It created curiosity. Luna: So the underline doesn't just emphasize — it creates a question in the reader's mind. That's a double whammy. Lucas: Exactly. And that's why it beat bold. Bold says 'this is important.' Underline says 'this is important — and you need to understand why.' It forces a micro-pause. Luna: Let's talk about the risk of overuse. In digital, if you underline too much, it looks like a link farm. You lose credibility. Lucas: Totally. The rule of thumb: one underline per piece of copy, and only in a headline or a key benefit statement. Never underline a whole sentence — just the critical two or three words. In the Boardroom letter, it was three words. That's the sweet spot. Luna: Have you ever tested this yourself in email subject lines? Lucas: Yes, with a client in the B2B software space. We tested an underlined subject line against a bold one. The underline lifted open rates by eleven percent. Not eighty-seven, but still significant. And the click-through rate on the underlined version was nineteen percent higher. The effect is real. Luna: So the underline works even in a subject line — something that's already short. That's surprising. Lucas: It does. But you have to be careful with email clients. Gmail and Outlook sometimes strip underlining from subject lines. So you need to use a Unicode underline character, or test across platforms. But in HTML emails, you can use CSS to force an underline on a span. Luna: Let's go back to the psychology for a second. Processing fluency — is that the same as the 'fluency effect' in advertising? Lucas: Very related. The fluency effect says that anything that makes information easier to process — like a clear font, high contrast, or in this case an underline — increases liking and perceived truth. That's why Bencivenga's underlined phrase felt more credible: it was easier to read. Luna: So in a way, the underline is a visual shortcut that says 'trust this.' It's almost subliminal. Lucas: Exactly. And that's what separates a good copywriter from a great one. A good copywriter knows what to say. A great copywriter knows how to make it look like it's easy to read. The underline is one tool in that kit. Luna: What about italics? Do they work similarly? Lucas: Italics are different. They signal a slight shift in tone — like a quote or a thought. But they don't have the same 'stop and pay attention' effect as an underline. Italics can actually slow reading because they're less legible. Underlines, on the other hand, don't distort the letterforms; they just add a line. Luna: So for emphasis, the hierarchy might be: underline > bold > italics, in terms of stopping power? Lucas: That's my experience, and the data from Bencivenga supports it. But context matters. If you're writing for a very formal audience, bold might be safer. Underline can feel a bit 'used car salesman' if overdone. But used once, it's a surgical tool. Luna: Let's give listeners a practical takeaway. If they want to test this next week, what's the simplest experiment? Lucas: Take your best-performing email subject line from last month. Rewrite it with one key phrase underlined — not the whole subject line, just two or three words. Run an A/B test with the same audience. Measure open rate and click-through rate. I'd bet you see at least a five to ten percent lift. Luna: And if you're doing direct mail — which I know some of our listeners still do — underline the benefit statement in the headline. That's the exact Bencivenga test. Don't change anything else. Lucas: Exactly. And if you're writing a sales page or a landing page, pick the single most important sentence — the one that encapsulates the offer — and underline the three most critical words. See if it moves the needle. The cost is zero. The potential upside is huge. Luna: It's one of those tweaks that feels too simple to work, and yet the data says otherwise. Lucas: That's the beauty of direct response. The small details — a dash, a comma, an underline — can be worth millions. Boardroom Inc. used that one underline for years across multiple mailings. It probably generated tens of millions in incremental revenue. Luna: So the next time you're tempted to use bold or italics, ask yourself: should I underline this instead? Lucas: And if you're worried about the hyperlink confusion, just make sure the underline is a different color than your link color, or use a non-blue underline. But honestly, the effect is strong enough that even blue underlines still work — because the reader's brain interprets the underline before it processes the color. Luna: That's a good point. The visual cue is faster than the semantic one. Lucas: Right. So our challenge to you: find one piece of copy you're using this week — email, landing page, even a social media post — and underline one key phrase. Track the result. Let us know how it goes. We'd love to hear if it works for you. Luna: And if you want to dive deeper into Bencivenga's tests, his book 'The Art of the Underline' — well, that doesn't exist. But his collected bulletins are available online. They're a goldmine. Lucas: That's it for today. Next episode, we're looking at a single word swap that turned a losing ad into a winner. See you then.