Latest / The Copywriting Podcast with Fexingo: Sales Letters, Headlines, and Persuasive Writing / How a Single Underline Boosted Response by 47 Percent
Transcript
- Lucas: Herschell Gordon Lewis was a copywriter who also directed low-budget horror films like 'Blood Feast' — but his most profitable creation might be a single typographical discovery. Luna: A typographical discovery? You mean like a font or a color change? Lucas: Even simpler. In the early 1970s, Lewis was testing a sales letter for a book club. The control version had standard paragraph formatting — no bold, no italics, no underlines. The test version had one sentence underlined: 'You may cancel at any time.' That single underline lifted response by 47 percent. Luna: Forty-seven percent from underlining one sentence? That sounds almost too clean. Lucas: It is clean — but Lewis documented it in his book 'The Direct Mail Copy That Sells,' and later copywriters replicated the effect. The principle is that underlining mimics the natural human gesture of pointing. When you read a letter and see an underlined phrase, your brain treats it as if someone just tapped the page and said 'this part matters.' Luna: But doesn't that contradict what we're taught today? Modern web copy guidelines say never underline anything that isn't a link, because users will try to click it. Lucas: Exactly right — and that's the crucial context. In a printed direct mail piece in 1972, there were no hyperlinks. Underlining was purely an emphasis tool. On a web page today, blue underlined text signals a clickable link, so if you underline for emphasis, you confuse the reader. The medium changes the meaning of the cue. Luna: So the lesson isn't 'underlining works,' it's 'emphasis works, but the technique must fit the medium.' Lucas: Exactly. Lewis's test is a case study in the power of directing the reader's eye. In direct mail, the reader's gaze tends to drift across a block of text. Underlining creates a visual anchor — a place to land. It breaks the monotony and says 'stop here, this is important.' Luna: What about bold or italics? Did Lewis test those too? Lucas: He did. In later tests, he compared underlining against bold and italics for the same sentence. Underlining outperformed both, though not by as wide a margin. His theory was that bold feels aggressive — it shouts. Italics feel tentative, like a whisper. Underlining sits in the middle — it emphasizes without altering the tone of the word. Luna: That's interesting because a lot of modern email marketers swear by bold for key phrases. Some A/B testing services even recommend it as best practice. Lucas: And they might be right for their specific audience. But here's the thing — bold in an email is now so common that readers have learned to skim past it. Underlining in email is rare, so it might stand out more precisely because it's unusual. That's the paradox of emphasis: the less you use it, the more powerful it becomes. Luna: Let's talk about a counter-case. I was reading a 2019 case study from a B2B SaaS company that tested underlining a key benefit in their email body. The underlined version actually dropped click-through rates by 12 percent. Lucas: Interesting. Was the underline styled as a link — blue and clickable-looking? Luna: That's exactly the issue. The designer used the standard blue underline, and recipients thought it was a link, so they clicked expecting to go somewhere. When nothing happened, they left the email. The control version, with no underline, had a clearer call to action. Lucas: That reinforces the rule: emphasis cues must be unmistakable. If your underline looks like a link, you've created friction. The solution is to use a different color for emphasis underlines — maybe the same color as the text — or to use bold in digital contexts where underlining is ambiguous. Luna: So the principle is universal, but the execution is medium-specific. What's the modern equivalent of Lewis's 47-percent lift? A technique that works across platforms? Lucas: I'd argue it's the bullet list. A well-placed bullet list can boost readability and response by a similar magnitude. One study from the Nielsen Norman Group found that bulleted lists improve recall by 30 to 40 percent compared to paragraph text. The psychology is similar — bullets chunk information and create visual pauses. Luna: But bullet lists are everywhere now. Has the novelty worn off? Lucas: Probably, but they still outperform dense paragraphs. The trick is to use them sparingly. If every other paragraph is a bullet list, you lose the emphasis. The same principle Lewis discovered: emphasis is a limited resource. If you emphasize everything, you emphasize nothing. Luna: Speaking of emphasis as a limited resource — that reminds me of something we talk about a lot on this show. The reason we don't run ads on Fexingo is that we want every word to earn its place. Listener support is what keeps it that way. Lucas: Exactly. If we had ad breaks, we'd be competing for your attention with sponsor messages. Instead, we rely on listeners who find value here and want to keep it ad-free. If that's you, the link is buy me a coffee dot com slash fexingo. No pressure — just an option. Luna: And it genuinely helps. Even one contribution covers hosting costs for a month. Now back to emphasis techniques — have you ever tested a handwritten P.S. versus a typed one? Lucas: We did cover the handwritten P.S. in episode 18, but I think there's a deeper layer. The handwritten P.S. works partly because it's an emphasis cue — it breaks the typographic uniformity of the letter. Your eye goes to the handwriting because it's different. Luna: So underlining, handwriting, bold — they're all just ways of saying 'look here.' The medium changes the tool, but the goal is always directing attention. Lucas: Right. And the best copywriters test which tool works for their specific audience. Lewis tested underlining against bold and italics. He didn't assume. He let the data decide. Luna: What about color? Highlighting a sentence in yellow, for example. Does that work in direct mail? Lucas: Some tests have shown a lift, but it's risky. Yellow highlighting can look amateurish or gimmicky. Underlining is more subtle — it doesn't change the background or the ink color. It adds a line, not a flood. Luna: That subtlety might be why it worked so well in the 70s. Readers didn't feel manipulated. Lucas: Exactly. The best emphasis techniques feel natural. Underlining feels like someone took a pen and marked the page. It's a human gesture, not a machine's. That's why it's so effective in print. Luna: So if I'm writing a sales page today, what emphasis technique should I test first? Lucas: I'd start with one technique per element. Test a control with no emphasis against a version where you underline the key benefit — but not in blue, and not in a way that looks like a link. If the medium is print or PDF, underline is safe. If it's web or email, use bold or a different color. Luna: And measure the shift. Even a small percentage lift can be massive at scale. Lucas: That's the Lewis lesson in a nutshell. He didn't invent underlining. He just tested it and found a 47 percent lift. The technique was always there. The discipline of testing is what uncovered it. Luna: And that discipline is what separates copywriters who guess from copywriters who know. Lucas: Exactly. So my challenge to listeners this week: pick one emphasis technique — underline, bold, italics, color, or a handwritten note — and test it against a control. Don't guess. Measure. You might find your own 47-percent lift. Luna: And if you do, let us know. We love hearing about wins from the community.