Having an alphabet, as it does, Korean indeed isn’t hard to learn to read and write. The difficulty is learning how to pronounce it properly—it has a number of distinct consonants that are treated as the same consonant in most other languages and that therefore are extremely difficult for non-native speakers to distinguish and produce properly.

For example, it has three distinct unvoiced velar stops [1] which are all considered the same sound in English: normal [k], aspirated [kʰ], and faucalized [k͈].

We use both the normal and aspirated [2] unvoiced velar stops in English as positional allophones [3], meaning we consider them the same sound but they’re actually different and we distinguish between them unconsciously depending on where the sound occurs in a word. For example, /k/ is aspirated in word-initial position in words like cam but unaspirated after word-initial /s/ in words like scam. If you listen closely enough you realize that you turbulently expire a lot of air after the c in cam but don’t do so in scam. Despite using both phones [4] in English, you consider them more or less the same hard k sound—if you pronounce cam with an unaspirated /k/ it may sound slightly odd but you’ll still consider it the same word cam. The problem is that in Korean doing so would result in two different words—so it makes it hard for English speakers to perceive distinct words in Korean that differ this way, and to pronounce the correct word that they intend when talking.

This is true for many languages because phoneme inventories never overlap, but it’s especially difficult for English learners of Korean because Korean has a third /k/ sound—the faucalized [5] one—and it doesn’t occur at all in English. I know phonologists—people who are trained in the study of human speech categories—who have an extremely difficult time discerning between [k] and [k͈].

Peter Ladefoged, one of the world’s foremost phoneticians, has a fantastic website to accompany his phonetics textbook and it has recordings of all the sounds known to be produced in human languages. You can listen to the distinctions between the Korean consonants here:

http://phonetics.ucla.edu/appendix/languages/korean/korean.h...

The /k/ sounds I’ve been discussing are the third row down (weight of measure, rope, and large). As an English speaker try to hear a difference between how the consonant is pronounced—it’s extremely difficult to notice.

Our sensitivity to these phonemic distinctions develops at an extremely early age: by one month old infants already begin to stop distinguishing between different sounds that their language slots into the same category as the same “sound” [6]. Infants don’t even babble at this age never mind produce or understand adult speech, but they have already stopped noticing certain differences in speech—that’s how deeply ingrained the way we perceive and produce speech is, and why it’s almost impossible to speak a non-native language without an accent.

(I am only tangentially familiar with Korean phonology so I might be getting some of the details slightly wrong here—please correct me if I’ve misstated anything.)

###

[1] http://en.wikipedia.org/wiki/Unvoiced_velar_stop

[2] http://en.wikipedia.org/wiki/Aspirated_consonant

[3] http://en.wikipedia.org/wiki/Allophone

[4] http://en.wikipedia.org/wiki/Phone_(phonetics)

[5] http://en.wikipedia.org/wiki/Faucalized_voice

[6] http://www.sciencemag.org/content/171/3968/303 & http://home.fau.edu/lewkowic/web/Eimas%20infant%20speech%20d...