SEM, or search engine marketing, is different from SEO, or search engine optimization.
For one thing, there is fairly broad agreement on what “SEO” means. Optimization, or making something the best it can be, for search engines, so making your website the best it can be at showing up when people search for things relevant to your business. This is about good content at your website, a high level of usability — stuff like that. It’s also about getting links to your website. Good quality links require good content, too, as well as regular linkbuilding, so linkbuilding is generally considered part of SEO.
SEM, on the other hand, may be anything that improves marketing using search engines. While some people define SEM as only paid search tools such as Adwords, others (include Wikipedia) would include SEO under the larger umbrella of SEM. I’d be inclined to say that important steps like printing your web address on your receipts or invoices qualify as SEM but not as SEO. Such a step can lead people to search for you no matter what your site is like once they get there (though it had better be good to bring them back).
The question is, can you manage with just one or the other?
Our experience with FreshPlans, our lab site, tells us that we can succeed with a site using only SEO. With nothing but a highly optimized website, we increased traffic to the site by 3,000% in a year. So yes, the answer might be that you can indeed make do with just SEO.
The next question is, are we talking about your lab site?
If your website sends business to your shop (or you want it to), you shouldn’t be experimenting to see how far you can get with just one approach when you could be doing more. Diverting traditional advertising dollars to paid search, advertising your website in traditional media, sending customers to your site, using social media to increase visibility — all of these are effective strategies for most companies.
So can you use just SEM? We’ve met people who use only paid search and ignore the quality of their site. We don’t get it. SEO is cheaper, more effective, and lasts longer than PPC, so why would you bypass it?
If you’re trying to decide between SEO and SEM, you’re asking yourself the wrong question.