A web developer can be a perfect web designer or a web designer can be a perfect web developer??

I think Web development is a logical filed which is totally different from web designing.. A web developer can be a web desinger but a web designer can't easily become a web developer 

Web designer can be a perfect web developer because design is every thing now in modern days not just the functionality, i just interviewed many developers they were not aware of the typography and perfect layouting to create dynamic applications and sites, it's all about the impression and eye catchy contents.

A designer lives in new ideas work while just a developer has no any attraction ideas to gather a traffic to his content and that's what i said better look is everything.

In my opinion we really need to understand what is good web design. I will consider a web design to be good if it's content is easily accessible. So let's start with mobile screen where theres is one eye and one thumb so content to be displayed accordingly, most important content should be displayed first. On larger screen we have wider real estate, so how you going to display content and adjust the white-spaces.

Why web developer aren't good designers because they use CSS as a toy language. I will back this statement by following story of mine

I worked with pure backend devs in, and whenever they were tasked with creating a layout to showcase their idea, terrible design would totally ruin their great idea. Thanks to the Visual Studio which came pre-built with bootstrap and saved those Backend developers.

Both can, but it's easier for a web developer since he/she has already some web design concepts.

Yes, A web developer can be a perfect web designer and developer he will design web page easily....but, a web designer can't be a perfect web developer---Coz a designer don't have much exposer on programming skills.

no it is  not necesary that a 

Mostly web developer are also web designer but the reverse is not true at all because web designing is not that much tricky as web development.

This depends on the field that the person  like

No a Web developer can not be web perfect web designer.

i think we developer can be a web designer

There are too many differences between the two specialists. A web developer can be a web designer because designing is the most important thing to become a developer because you have to layout your application and web designer is 30% can be a web developer because the designer is totally different and easy.