Today you’re going to learn about Latent Semantic Indexing (or LSI).

This is a phenomenal SEO strategy that you should be using in all of your SEO copy.

If you have any URLs out on your website that you want to rank higher in search engines, and they’re not quite there, you absolutely should be applying Latent Semantic Indexing principles to your copy.

We’re going to talk about exactly what Latent Semantic Indexing is, how LSI works, the fastest way to implement it on your own site, and how to get that going right away.

What is LSI?

Latent Semantic Indexing (LSI) is really just a fancy way to say “additional relevant keywords”.

The term is relatively new to the SEO world, but not as new in the academic world. In fact, Latent Semantic Indexing and Latent Semantic Analysis have been around since the late 1980s, dealing with natural language processing and distributional semantics. Basically, what they did back then was creating a matrix out of a large text and using a mathematical technique (singular value decomposition) to analyze the relationships between two documents and terms they contain. In 1988, Susan Dumais, George Furnas, Thomas Landauer, Karen Lochbaum, Richard Harshman, Lynn Streeter, and Scott Deerwester patented an information retrieval technique using this method.

The same basic principles apply in SEO Latent Semantic Indexing as well. Search engines use an information retrieval technique to analyze the terms in documents, and this helps them populate SERPs with the best options for users.

Google has a very difficult job in trying to rank documents. When a user does a search on a search engine, Google has to find the 10 most relevant documents to show on this first page of results for the given search terms, and LSI is really just a way to help them do that.

LSI is a super-important part of copywriting these days, specifically copywriting that’s beneficial for search engines.

The basic idea here is that there’s a number of keywords that do not necessarily fall into the synonymy category, but are incredibly contextually relevant to your primary keyword.

Before we dive into this, just a quick reminder: this is a component of Search Engine Optimization (SEO), and SEO is only one piece of digital marketing.

We’re going to be diving specifically into one SEO topic today (as mentioned above, LSI), but just keep in mind that your entire digital marketing strategy should be composed of much more than just Search Engine Optimization.

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SEO copywriting basics

It’s important to understand the basics a little bit before we dive more into LSI and what it is.

So, let’s say I have a website and I’m trying to rank a page on that website for a particular keyword.

What are the things that I need to do to get that page ranking?

From an on-page optimization perspective, the very basic thing to do is using the primary keyword exactly as it’s written about two or three times in your document.

Google understands synonyms related to that keyword, so go ahead and sprinkle a couple of those in the copy where it’s reasonable.

Remember, you’re writing this for humans, not search engines.

I made this massive mistake when I first got into Search Engine Optimization: I would design my copy for search engines, not for users. That means I wrote very, very spammy, gross-sounding copy.

It sucked—so don’t do that. Make sure that you’re writing your copy for humans.

What I like to do is actually write my copy first and then go back right before I hit publish and do all of my SEO tweaks (getting my primary keyword in there two or three times, getting some synonyms there a couple of times, reading it all out loud before I publish).

I generally find much better results in doing it that way. If it sounds terrible when you read it out loud, you’re doing it wrong—so re-work it until it sounds great.

How to use LSI keywords for SEO copywriting?

Once you’ve done your core copy, you’ve added your primary keyword and some synonyms in there, you will want to look at Latent Semantic Indexing keyword research.

LSI is just a fancy way to say “other contextually relevant keywords”. It’s consisted of words that are thematically related to your core keyword.

For example, if my core keyword was “Empire State Building”, some other synonyms for “building” might be “tower”, “skyscraper”, or “high-rise”.

Latent Semantic Indexing keywords would be words that are thematically related, but not synonyms.

In the “Empire State Building” case, it would be keywords like “New York City”, “Guinness Book of World Records”, “sightseeing”, and so on.

Those are not related to a building at all, but in all these other pages that are out on the web that are mentioning the Empire State Building, “New York City”, “Guinness Book of World Records”, and “sightseeing” are consistently coming up.

There’s a thematic relationship between these phrases.

The idea here is you can signal that document relevance to any search engine crawling your documents, if you have a lot of these LSI keywords in there.

How to find LSI keywords?

There are a couple different ways to figure out what your LSI keywords are.

My first and favorite way is Basically, you plug your primary keyword in and it will render a bunch of results for you that show you Latent-Semantic-Indexing-related keywords.

To use this tool, go to, input your primary keyword in the search box and then click “Generate”.

In my example below, I entered “Empire State Building” and the LSI Graph tool gave me all these keywords it thinks that are related:


These are not synonyms for “building”, but the entire universe of possible documents that might contain the words “Empire State Building”.

The basic idea here is that LSI keywords are useful from a document relevance perspective. I want to add as many of these into my document as possible.

Keep in mind: same keyword-usage rules apply here as well. Make sure to read your copy out loud. Don’t include anything that’s not great for users.

You want to signal that document relevance, so if you can, add as many LSI keywords into your document as possible—but keep it user-friendly at all times.

Another great tactic people frequently overlook is Google: Just Google your keyword.

Once you’re in the results, scroll down to the bottom and go to the “Searches related to…” (in my case, this was “Searches related to Empire State Building) .

printscreen of a google related search suggestion

Google actually gives you these answers. It thinks those queries are related to your initial query.

For example, I Googled “Empire State Building” and I got “Empire State Building ticket prices”, facts, floors, history, hours.

This particular search query might not be a great example for LSI because there are a lot of navigational queries in here. But sometimes, just Googling the keyword works very well.

That’s it. That is Latent Semantic Indexing or LSI—keywords that are not necessarily synonymous to your primary keyword, but rather contextually related to it, and which will help search engines better determine what your content is about (thus, pushing you higher in the SERPs).

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