Rule of thumb: 1-syllable words: add -er (or juse -r if the word ends in 'e') 2-syllables words: if they end in -y, replace -y with -ier; if not, use "more." There are a few exceptions. Like 'simpler', 'narrower', 'quieter', and, in some instances, even 'cleverer'. Although, on a whole, the double 'er' ("erer") is just awkward. "Quiet" doesn't have that problem. Language is never about applying strict grammar rules, though. You can easily say either of these: "Let's go to a quieter place." Or, "Let's go some place where it's more quiet." The following, however, really sounds forced: "He's cleverer than him." Especially since 'cleverer', when you talk about people, is if not wrong, then certainly not preferred; "He's smarter than him." is much better. "Cleverer" really is only something you say about things, like: "There's got to be cleverer ways of doing this." That sounds perfectly normal again. It's subtle, but distinctly there. And the next, too, sounds very smooth and natural again: "It's simpler than that!" N.B. Indeed, 'safe' as a noun doesn't mean 'more secure.' Only when used as an adjective or adverb: "He is safe now." Or: "That's a safe way to procede." Oh, and in Marie's usage of "more safe," 'safe' is not a noun, either; much like "more beautiful" doesn't make 'beautiful' a noun either. :)

Although a lot of native speakers would actually use safer in casual speaking, more safe is grammatically correct

Safer might be used more often, but there are phrases where "more safe" is used as well. Also the noun form for "safe" that means "security" is "safety." "Safe" used as a noun refers to a locked, metallic and heavy container to put valuable things in. Ex. "I put all my expensive jewelry in a safe."

Hi... you have to say "safer" but the other one help you explain ... that's all.