How to know if the melody you composed has not been used before?

I ask this because I am working over a piece and two melodic phrases were composed that sound so perfect and simple that I have the feeling I heard that before, same a friend, but we can't determine where. So I also thought in the possibility that if something is so perfect for our human hearing, it could be recognized by us like familiar. Those melodies are of those that don't need any note to be changed, they sound round and the feeling is logical and with sense, there are several in history, pop music included. But I as I am not sure, and therefore this is still a possibility, how can I know?. I am not going to earn money with this, but I don't want to copy others work. 

Has this happened to you?. What do you do?.

rgds,

That happens to me occasionally too.  If I can't figure out why it feels so familiar, I write it out and post it here and on social media before I get too far writing a piece of my own based on it.  About 5 people usually pop up right away to tell me that it's the theme from "Sleeping Beauty," or whatever.  There have been one or two melodies that everyone agreed were very satisfying tunes, but no one recognized.  In those cases I feel comfortable creating a piece around them.  If it does turn out that I've accidentally copied and re-harmonized a little snippet of Vaughan Williams, I can rest easy knowing that I really did my due diligence to avoid doing so, and since I'm not intentionally copying a piece, note for note, my resulting work will end up being more of an appreciative quoting of someone else's than a straight copy.  That's a thing that happens frequently in music and is generally accepted as fair use and flattering to the original composer.  

Post a snippet here, and see if anyone recognizes it?

This happened to me before. I once got a melody into my head and it sounded perfect. It also sounded familiar. I soon got over its familiarity and was about to write it in my composition when I heard it playing on the radio. It turned out that it was from Schubert's Symphony 5 and that the reason that I thought it could have been from The Magic Flute Overture was because I went to a concert that had both of them in.

"Lesser artists borrow, great artists steal." - Igor Stravinsky.

Even you did unconsciously recreate a melody that was someone else's, just know that you are in good company.

pateceramics : Here the demo attached, the two melodic phrases separated by a silence. Please put attention only to the melody, not the left hand, it is not worked at all, just to demnostrate I used basic stuff and almost no variations.

thanks guys for the comments.

Like @bkho said, I wouldn’t worry too much about it, as long as we don’t talk about plagiarism. Think about „Viva la vida“ from Coldplay, which was a major hit nine years ago. Joe Satriani and Cat Stevens both claimed the song to be based upon one of their songs, as did the band Creaky Boards. Satriani’s claim even escalated to court. However, it was shown that the songs of Satriani, Stevens and Coldplay (and by implication also the one from Creaky Boards) share essential features with a aria attributed to Pergolesi, a composer from the 18th century. Some allege the song was really written by the historian editing it in the 19th century, but either way much before Coldplay or Cat Stevens.

Also, it was always usual for composers to take other’s pieces as inspiration. Some took this even to the level of an intellectual game where the conoisseurs could find citations out of works from other composers, much like in some movies, where subtle references to other movies are woven in for the cinephiles. Some allege that e.g. Händel and Telemann incorporated themes from each other in their work as a sign of mutual admiration. Also, some themes became something like “household melodies” that were used again and again on purpose. The craft then is not the theme, but what is done with it, how it is presented and elaborated.

There fits another story: When Werner Heymann wrote the German evergreen „Das gibt’s nur einmal“ - (there is an English version too: Just Once For All Time - to be heard after a few minutes in this clip: https://www.youtube.com/watch?v=iahDZzixaJE) - he was so afraid it could be accused of plagiarism that he went to all major music publishers and played the song to them, asking if it reminded them of one of their hits. However, all publishers said they wouldn’t know a similar song, so he could offer it for an upcoming film and it went on to become an international hit in the 30’s.

@Donethur Your two passages remind me in an instant of dozens of works - but I mean this in a very positive way. No one could accuse you of plagiarism if you use passages that are part of the (advanced) musical vocabulary. To repeat myself: I think it is more important what you do with these passages instead of how original the basic content is.

Donethur, your opening follows a common harmonic progression in many classical works so that's why it probably sounds so familiar.  I wouldn't worry too much about it.

Thanks mates. I will keep working over them :). I have a lot of small parts of the same piece already composed but this will be a lot of work (also I need to work over variations), I hope this will  be a good one. Rgds,

I also think it deals with the progressions, heard thousand of times before...

Paul McCartney wrote 'Yesterday' that way.. Although It was called 'Scramble Eggs' for  a while cause he didn't have the lyrics..  He constantly played the melody for everyone he know. Cause he wasn't sure if he came up with it, or had just heard it before..  No one could identify it.  George Harrison, and Lennon got sued, (and lost) for 'unconscious plagiarism'.. Harrison had to pay a hefty fine.. Lennon recorded an album of old rock covers, that the publisher owned all the rights too.  Worked out well,  Lennon got a classic album, the Publisher made a ton of money because a 'Beatle' had done versions of all these great rocker tunes from late 50's  - 60's. 

I hear Tv ads for cable stations, were it really feels like conscious rip-offs of earlier melodies.  Because it's local cable, I doubt the copyright holders, ever got to hear it. 

One of John Legend's earliest hit was a 'direct ripoff' of a 60's song by 'The Classics IV'.  Of course Sony probably owned the publishers to the earlier song.  

My attitude is, as long as it is not a obvious rip-off.  use it.  if it ever becomes an issue..  A publisher is not going to spend the lawyer and court costs, to wheedle a small amount out of you.  Having a strong mind, and 59 years of musical memory..  I can point out a lot of situations, where a melody fragment, resembles (sometimes closely) to something earlier.. Truth is 

there are really only certain combinations of notes which work well and are membeable l with a certain chord progression.. so there is always going to be similarities, even close ones, cropping up.