There are a lot of words used in everyday conversation which have no precise, defined meaning. A prime example occurs in the previous sentence. How many is a lot? Ten, a hundred, a thousand? The extent to which these words are vague and ill-defined is a variable in itself but a further example definitely occurs in the consideration of the differences between hills and mountains and what factors or features distinguish one from the other. There does not appear to be a precise answer to this conundrum but this page is about exploring some potential factors which can be considered. 

A Bleak Mountain Landscape in the Austrian Alps

The Austrian Alps
Credit: Gordon Hamilton

This picture was taken near Innsbruck in Austria from a vantage point which had to be reached using two separate cable cars

The Height of the Feature

One of the most common answers likely to be given to this question is that mountains are higher than hills. This is probably a good measuring stick but is entirely open to interpretation. Might it be fair to say that while a hill can be climbed and descended on a fine summer's afternoon, a mountain can require a whole day minimum and possibly considerably longer to scale?

How Steep is the Feature?

It would not be expected that any specialist equipment would be required to climb what is commonly thought of as a hill. In the case of a mountain, however, specialist equipment such as ropes, crampons and more would commonly be thought of as being required to make the ascent possible. 

Cable Car Ascending Mountain in Austrian Alps

Vertical Cable Car Ascent
Credit: Gordon Hamilton

This mountain was so steep in places that this part of the cable car ascent through patchy cloud was almost vertical

Are the Feature's Slopes Grassy or Barren?

Although not such an obvious consideration as height or the level of steepness, might it not be the case that hills are often considered to have grass covered slopes while mountains are more likely to be thought of as rocky and barren? Thinking of The Sound of Music compared to Heidi perhaps illustrates this example quite effectively.  

Scottish Scenery at The Rest and be Thankful

The Rest and Be Thankful
Credit: Gordon Hamilton

This beautiful example of glacial erosion scenery is The Rest and Be Thankful in Argyll, Scotland

Glacial Erosion versus Water, Volcanic or Seismic Activity

There are a number of potential ways in which hills and mountains were formed in the distant past. If they were formed by glacial erosion, the valleys between the features will be u-shaped and gently sloping, perhaps more commonly seen between hills? If water, volcanic or seismic activity was responsible, the valleys are more likely to be v-shaped and and the landscape in the latter two instances at least more harsh, perhaps as a result more commonly attributed to mountain vistas? This possible distinction is perhaps the least reliable but can undoubtedly be applied in a great many instances.

It may be that at some future time, a particular scientific body will produce a definitive guide to the differences between hills and mountains but until then, the matter will remain open to interpretation and continue to vary perhaps significantly depending upon individual opinion and interpretation of the evidence.