Is it possible to learn graphic design by myself or is it more beneficial to take certified graphic design courses?

If you are talking about Graphic Design tools and techniques like Photoshop, you can learn that wether on your own or within a courses, but with courses you'll save your time.

But if you'r talking about the Design Principles, concepts and processes. This something you can not learn it by yourself, you need to participate in workshops and have someone to criticize your work. 

Yes, you can learn graphic design by yourself especially now that information come in handy through the internet.  But taking up design courses in schools has a lot of perks that you may not easily have alone. I'll break them down for you.

In school...

1) teachers have organised syllabus to offer you.

2) you have access to facilities and libraries.

3) you can easily build your network.

4) you will be up to date to local and international art activities.

5) you will learn fast because everything is time bound. 

6) constant competition will bring out the best in you.

7) by the end of the day, you'll have a certificate or diploma which you can flaunt as a laurel and nobody else could question your expertise at all because you've gone through an institution's standards which many people take as a reference in prejudging others.

The downside though is it's not free. :(

Yes, you may have to take certified graphic design courses if you are going to get a job in a company.

i prefer to take courses to learn how use the applications but you can go over youtube and looking behind your needs step and step.

Yes, You can learn GD on your own, it has advantages and disadvantages, but learning in a certified GD school is so much more beneficial.

Learning courses and diplomas will give you the tools, Designing and Creativity you have to find it with your self by Self learning, Practices and Experience.

Graphic design is a very wide & general word, you should first specify your career which it may be web designer, advertiser, or even an architect & depending on your career we can specify the best way for learning 

Learning depends upon your passion. IF you are passionate about learning graphic design, these days its is possible to learn by our own as there are lot of videos which will support in your learning.

But it is always recommended to get a certified course done for two reason;

1) It will add to your resume

2) You do not think of everything when it comes to learning and hence professionals would come handy to learn everything in graphic design. i.e Professionals will make sure that you are master in the concerned field.

well in case of myself

I never learned from any school about computer or graphic deigning,

but i trained four persons,

they are now working in field

one of them is in behreen

the point is how creative u r

& how much ability u hv to learn things quickly

i learned alot from YOUTUBE

it is now biggest university to laern any thing,

from hair cutting to engineering youtube helps everyone,

i'm a graphic designer since5 year but i'm student of youtube till now

Well you can learn graphic by yourself and having the certificate is another thing of desire.

Its same like a kid going through school and learning all the phases, on other side if you try learning by yourself no doubt you'll end-up learning many things of your interest. But the most important thing is to  improve one-self in a most organized way i would suggest you must go to some basic/advanced level GD course.  Start picking up things and take your career on high peek.