Context Is Important

The primary reason  you can’t learn Spanish using the phrase method alone is that it lacks context.  The human brain is amazingly adept at retaining information that has some meaning in relation to something else.  That is, remembering the phrase “¿Donde está el baño?” is going to be far easier if you really, really have to pee or the phrase appears within the context of a funny anecdote.  That way, whenever you have to use the restroom you will associate that experience with the correct Spanish phrase and vice versa.  This is a stupidly-simple example, but the principle is clear, I think.

Don’t get me wrong, I highly recommend the phrase method as a great way to expand your Spanish vocabulary on the side, but it should not be your primary method of study.  Your primary method should ideally be a structured program such as FSI, Pimsleur, or Rosetta Stone that guides you all the way from a beginner to the advanced stages.  After all, you aren’t the first person to want to learn Spanish.  It’s been done before, and there are certain techniques that have been shown to be more effective than others.  Basing your studies around a good, well-researched, structured program will save you both time and money over the long run.  Contrast this with the haphazard nature of the phrase method.  Sure, you’ll learn a little bit and may even be impressed by your progress at first.  But there is nothing at the core of this method to help you put it all together.  How do you relate one phrase to another and form new, abstract thoughts if all you’ve ever done is rote memorization?  You probably can’t.

That said, I do recommend getting yourself a good, inexpensive phrase book as a way to expand your vocabulary.  You might also want to try vocabulary cards, which have advantages of their own.