Describing values as being 'assumptions' or 'assumed' - what is the correct approach in academic papers for civil engineering?

I am a language editor of academic papers in civil engineering (typically written in English by Poles).

I frequently encounter the term 'assumption' being used to describe a value that is adopted for the sake of calculations. For example, an author might not precisely know the original thickness of a corroded steel shell of a silo, but makes a decision about what it might have been in order to perform calculations/modelling. This would typically be written as something like: "assumption for thickness of steel shell = 6 mm".

I really feel uncomfortable with words like 'assumed' and 'assumption' on the basis that they are, almost by definition, unscientific. What would be the correct way to describe the above example?

Engineering has been defined as "the art of reaching the correct conclusions from insufficient data".

Everything an engineer does is based on assumptions and approximations. Most of them are never explicitly written down, otherwise papers would be ten times longer than they currently are.

It would make no difference to the conclusions of the paper if the engineer took some expensive 3D measuring equipment to the silo, and measured the profile of the entire corroded shape to an accuracy of say 0.1mm, and then made a 500,000 degrees of freedom structural model of every tiny bump. And even if that was done, the material properties used would be "assumptions", unless a sample of the material from the silo itself was tested. And of course the effect of corrosion on the material properties of every bump would be different. And so on, to infinity...

• Thank you - it's really valuable to have the opinions of people who clearly know what they're talking about with this - much appreciated. Jun 15, 2019 at 9:19

Why are "assumptions" unscientific?

Many many problems are solved by stating things like :

The density is assumed constant,

The pressure is assumed constant

So, there is nothing wrong with "the original thickness of the steel shell is assumed to be 6mm" or variation thereof.

And, perhaps guessing the direction of the paper(s), assuming an original thickness to predict the rate of corrosion so as to be able to estimate the lifetime or the strength of the steel is very relevant to some engineers.

• Thanks Solar Mike - you've added a lot of clarity here and made me feel more confident about how I approach such situations - ta muchly. Jun 15, 2019 at 9:21

There are a lot of assumptions in science. Thing is most of us dont notice these assumptions because people leave them out. Does not mean assumptions are not there.

I can guarantee that a lot of the physics formulas you were given at any level of school had some simplifications associated with them, you just missed that section in the text.

Now if you introduce a new formulation of something it is prudent to tell what simplifications of reality you made. So using a sentence with a assumption is a perfectly normal way to do this. This way the reader knows wether or not the simplification is suitable for them. In fact leaving this out, except for cases where the assumptions are grandfathered from known formulas, is not very engineringly or scientifical for that matter.

Both engineering and science is to a great extent about honesty to yourself and others. Not documenting it as such is dishonest. There is nothing unscientific about simplifying reality, in fact that is what science is.

• Thank you, @joojaa - that makes a lot of sense Jun 16, 2019 at 8:00