Is it enough just knowing how to play a guitar?

By "knowing how to play" what do you mean? Is it purely strumming the guitar without melody or the real music accompanying through guitar? Well, I think it would be much better to know some notes and of course the chords that go with them for the guitarist to be effective and nice to hear when playing. To be able to know how to sing is just a bonus.

It all depends on what a person wants to get out of playing their guitar (or any other intrument). If playing simple 2 or 3 chord songs makes him happy, then he is getting what he wants out of playing. He isn't alone with that.. there are a lot of really famous guitarists out there who can't seem to play any better than your friend. I teach guitar myself. The motto on my business card is, "When you're ready to learn guitar, not just songs". If someone calls me asking for lessons, but all they want to learn is how to play tabs or songs, I refer them to Fretplay.com or some of the other online tab sites and wish them well. However, if they want to learn how to play the guitar, I'm happy to give them lessons.

I love learning new songs and new chords. My friends on the other hand like to just play but they don't want to learn new chords that are bar chords and that drives me up the wall. There are so many great songs that use more than just the simple basic chords but they don't want to take the time to learn. I get right on the case and make them at least try. I got them doing about 4 bar chords now and our number of songs has increased by more than double. I have even stopped going to the jams because they won't learn new stuff. That seems to work because after about a month they call me and promise to learn new things. :)

Playing basic triads is enough as long as your friend doesn't plan on a serious music career. Most pop songs don't have more than a chord or two to them anyway. Your friend could always take guitar lessons.

Actually it isn't if you have the urge of becoming a great guitar player. But if your not that into it its fine if you only know the basics. Its the more you play the more you get good skills. Simply holding your guitar and playing, its a form of practice already and eventually your skills would improve.

I think, like any instrument or skill, playing the guitar takes time and practice devoted to it. You're not going to get better unless you practice every day and keep the skill fresh in your mind. It's crucial with anything you do and that you want to become good at. The age old saying says, "Practice makes perfect."

It really depends on how much skills in "playing the guitar" you want to learn. I think it has something to do with one's passion for music. It would be better if you can also sing the songs you play. It's a great way to relax. I used to play the guitar but i haven't played for quite some time. But still i remember the chords when i play a song. It's not really memorizing the chords but it's the tune that you need to feel. I don't know how to read notes also. Just memorize the Majors, Minors, Sharps, and Flats and once you get a feel of the tunes, you can play any song you that like even without the chord chart.