Thank you very much Ken for this comprehensive answer. The Horstobel Sachs system has always been hard for me to wrap my head around, but what you typed is super easy to grasp. Would any discontinuous fretboard then be considered a lute? 

That's true Dusty. What was it that guy in England said, "A rose by any other name will smell as sweet?" Perhaps a dulcimer by any other name still has a sweet sound.

Ken

"The dulcimer sings a sweet song."

Let's remember that the distinction between the lute family and the zither family is based on organology, which classifies instruments based on the way they make sound (technically its the Hornbostel-Sachs system). 

There are certainly other ways to classify them: how they are played, what they sound like, the purpose of the music (dance, worship), etc.  After all, in terms of organology, the piano and the organ are completely unrelated instruments, the former a string instrument and the latter a wind instrument.  But most of us see them as similar because they are played in a similar manner.  In terms of how you play the instrument, the mountain dulcimer is much closer to lutes than to zithers such as the hammered dulcimer.

Well, Nate, I'll attempt to answer your question about the instrument in the photo using the Horbostel-Sachs classification system for musical instruments. In this system there are five categories of instruments. The one in the photo is clearly a chordophone; it has strings. There are five types of chordophones; bows, harps, lutes, lyres, and zithers. I think we can agree it is not a bow, harp, or lyre which leaves us with or question; lute or zither. If the fret board can be detached from the box (resonator) and still make a sound, it is a zither. If no sound can be heard after the two are separated it is a lute. Think of it this way. If you take the neck off of a guitar, ukulele, or mandolin you can no longer strum the strings thus you have no sound. (You could hit the box and make a sound like a drum, but then it is no longer a chordophone.) If you remove the box (resonator) in your photo, you can still get a sound from the fret board (although muted), so it is a zither. Further refinement of the definition is difficult in this system although it likely would go under the category stick zither.

Ken

"The dulcimer sings a sweet song."

This is an age old discussion that has been going on for far longer than the 30 or so years I've been into dulcimers.
Is the "neck/fretboard extending beyond the sound box" what defines a mountain dulcimer? Or is it the diatonic fret arrangement? Or is it the number of strings or the double melody course? Body depth and shape? The tuning? We've debated all this forever (in a good way)  :)   With so many tweaks possible in various combos, at what specific point does an instrument change from being a zither, a dulcimer, a lute, a cigar box guitar, etc. Is a guitar with diatonic frets a dulcimer?  Is a mtn dulcimer with a calfskin resonator insert a banjo? Is a stick dulcimer really a dulcimer?- if so, is it still a 'dulcimer' if it's chromatically fretted, or not fretted at all?

"What makes something a dulcimer" has always been a complex question, especially when so many hybrid instruments come on the scene. Often it just comes down to "what to call this".

But there's no 'rule book' -except the generally accepted definitions of musical instrument categories (lute family, zither family) that we've already cited. People can declare what is or isn't a mtn dulcimer til the cows come home, but often it comes down to opposing opinions.

It's hard to differentiate the concept of a dulcimer from its fretboard and string layout. A three course instrument with a paired melody course and two accompanying courses in the same key is such a powerful concept that it gets applied to all kinds of different resonators. 
On the topic of lutes and zithers, I am wondering how this system reconciles something like a discontinuous fingerboard which terminates before the bridge, or a dulcimer with a fingerboard that extends beyond the box. Is the following photo a lute or zither?

Thank you Strumelia. I will try that.

Strumelia,

Key of D

I agree, Dusty. The main problem is that there are so many styles from Martin's Backpacker Guitar (because it has 6 strings) and McNally's Strumstick® (3 strings) to the Merlin and homemade instruments with three or more strings. An additional category might include fret patterns. So, do we put our collective minds together and start working on this?

Ken

"The dulcimer sings a sweet song."

Marsha, what key do you want to be playing in?  Then we can tell you what tuning to use if you want to be playing with that 'medieval sounding' aeolian mode... either with or without using a capo.

Thank you all for the interesting feedback. I may be wrong but am thinking that watching other videos from that guy I saw that besides using the capo on fret 1, he also had a slightly different tuning from DAD (I can’t remember, but maybe one of the D’s was one step different?)

I guess I will just stick to relying on using that E minor to get a more medieval sound. I was talking to my husband Mike about it and suggested that the next time he gets the urge to build another dulcimer for me (he has built 7 so far experimenting on different  woods and designs) that he do a pear-shape that looks like a lute just for fun.

Well OK, so lute might be the genus, but we still need a species name.  

In the lexicon of stringed instruments the lute is characterized not by the number of strings but by having a sound box (often pear shaped) and a neck over which the strings extend. As Strumelia points out I should have be more precise by saying "lute family" rather than just lute. And the ukulele is a member of the lute family. You are correct about the Seagull instruments not having a 6 fret as they are intended to be play in a 1- 5 - 8 tuning.

Ken

"The dulcimer sings a sweet song."

There might be some confusion here between referring to "a lute" and referring to a member of the lute category of instruments... being a sound box with an attached neck and strings going over the length of both. Guitars and mandolins are in the lute family. And the zither family being a usually flat sound box without a neck, and strings going the length of the sound box. The mountain dulcimer and the hammered dulcimer are both in the zither family. (according to the Hornbostel–Sachs instrument classification system)

It may not be a dulcimer, but it isn't a lute either.  A lute usually has 11 or more strings. I believe a Renaissance lute has 15 strings, and some courses are not fretted but only used for bass notes.  The instrument in the video is more like a diatonic ukulele than a diatonic lute. 

@ken-longfield is on the right track referring to it as what is often called a stick or walkabout dulcimer.  The odd thing about Seagull's Merlin is that it has a 6+ fret but no 6 fret.

As Strumelia so graciously pointed out, that is not a dulcimer. It is a lute with a diatonic fret board. Seagull makes an instrument similar to the one in the video. At one time it was called a Merlin. Looking a Musicians Friend, I see they are called Seagull dulcimer. Do a search there and you will find several models. There is a used one for under $100. They should be easy to build. Michael J. King has a book, Stick Making Dulcimer Book, available on his website: michaeljking.com . He is in Great Britain. I think he also has plans you can download.

Ken

"The dulcimer sings a sweet song."

In that video, he is simply putting a capo on fret 1, which changes you to Aeolian mode. Aeolian mode sounds minor and gives you that 'ancient' sound that you are liking as a medieval type sound. But you can put a capo on fret 1 on any mountain dulcimer and get the same thing and play the same music he is playing in the video.... did you know that? 
Unless what you are wanting is the lute-like SHAPE of his instrument, including the neck and the bowl-like body shape. In that case there are several makers of 'stick dulcimers' (dulcimers with necks, technically making them be part of the lute family, rather than the usual zither family of instruments). Stick dulcimers can be found that are not very expensive- try searching for 'stick dulcimer' instead of 'lute dulcimer' and you may find some makers that meet your taste and your budget.

Have any of you ever played or built a Lute Dulcimer? I saw a YouTube video that   fascinated me as I love playing Celtic and medieval tunes. I would love to buy one but they all look way too expensive. My husband built my mountain dulcimer and I am looking for maybe some plans and instructions for him to build me one.

If you want to check out the video: https://youtu.be/u814RNCqxEQ?si=kICcja0RAcyLi68K