# extrapolate vs conjecture

Are these verbs can used interchangeably in the sense of "to guess based on some information".

The remains are conjectured to be thousands of years old.

He conjectured that the company would soon be in financial difficulties.

We'll never know exactly how she died; we can only conjecture.

The figures were obtained by extrapolating from past trends.

You can't really extrapolate a trend from such a small sample

These are example sentences I got from the Oxford and Cambridge online dictionaries.They are original sentences.I wrote down many examples to make it easy to compare for ones who would like to answer this question.You can give your own examples as well if you want.

• Extrapolate has the sense of estimating unkown data points based on known points, like extending a graph into the future based on the points measured in the past. Conjecture is more just guessing based on what you know. – ColleenV Feb 10 '15 at 13:18
• @ColleenV Thank you for your answer. Can we say there is a grey area for the usage in some sentences? Would you replace these words in the example sentences? – Mrt Feb 10 '15 at 13:32
• Murat - It's English. There's almost always a "grey area" for some usages :^) – J.R. Feb 10 '15 at 14:04
• @J.R. Yeah I agree with you but the question is actually how grey it is :) – Mrt Feb 10 '15 at 14:11
• You can conjecture what an extrapolation might imply, but you can't extrapolate from a conjecture. You need a set of related facts that show a trend to extrapolate. A related word is interpolate, where you guess a missing point in a set of points based on the points around it. – ColleenV Feb 10 '15 at 14:33

"Extrapolate" is a mathematical term meaning to extend a graph based on known data points. To take a simple case, if you had a graph with the points (1,2), (2,4), and (3,6), these would form a straight line, so you could "extrapolate" by extending that straight line indefinitely. In more complex cases you might say that the points form a parabola or a logarithm curve or whatever, and extend appropriately.

More generally, then, "extrapolate" is used to mean to predict the future based on current trends. This could be in the strict mathematical sense. Like someone might say, "The number of cell phones in the world is increasing at such-and-such a rate, so if we extrapolate from this, within ten years there will be more cell phones in the world than people." It is also used for more general predictions where you couldn't really measure or count. Like, "At the rate that this country is sinking into moral decay, within 20 years we'll be debating whether people have a Constitutional right to rape a 6 year old."

"Conjecture" is a far more general term meaning to speculate or estimate. The connotation of "conjecture" is that it is an informed guess. That is, it's not wild speculation, but it is also not based on any solid evidence. Like if I said, "I think the stock market will go up 20 points next week", you'd probably say that is a wild guess, because I know very little about the stock market. But if an expert stock market analyst said the same thing, you might call that a conjecture.

Proposed mathematical theorems are sometimes called "conjectures". That is, if a mathematician says that intuitively to him, he thinks that some statement about numbers or geometry or whatever is probably true, but he hasn't been able to devise a proof, that is called a conjecture.

• Thank you for your answer .This is a super-duper answer. – Mrt Feb 10 '15 at 17:21

"Extrapolate" implies a mathematical (or pseudo-mathematical) basis for the claim, and is in the nature of a prediction, along the lines of "If this goes on, such and such will happen". It usually falls short of actually being a prediction, since it is usually dealing with a specific set of observations, and those observations may not take into account underlying processes. Extrapolating population growth, for instance, usually leads to projections of impossibly high population sizes.

"Conjecture" is more of a speculation. It is not based on numbers, and is much more tentative than "extrapolate".

• Thank you for your answer. Can we say there is a grey area for the usage in some sentences? Would you replace these words in the example sentences? – Mrt Feb 10 '15 at 13:28
• I don't see a grey area in the examples. Note that extrapolate is used with respect to a (presumably measured) trend, or a specific sample. At some point, the description of a trend will get fuzzy enough for extrapolation to shade into conjecture, but that line is pretty fuzzy itself. – WhatRoughBeast Feb 10 '15 at 13:36
• I think I got it a little better and I think , it is very general comment, I can say "to extrapolate" has meaning like "to predict", because the word predict sounds like for me,you need factual things , on the other hand the word " to conjecture" have a meaning more like " to guess" generally which you can guess even without an evidence just with assumptions. – Mrt Feb 10 '15 at 13:50
• But I think I remember I came across the word "conjecture" in a context which was about statistics and prediction for future – Mrt Feb 10 '15 at 13:54
• A conjecture can be based on numbers though. If I look at say employment rates in an industry and compare them to graduation rates in certain degrees, I could make a conjecture about whether folks with certain degrees end up working in the field they studied. I would actually have to design a study to test my conjecture, but the conjecture is still based on numbers. – ColleenV Feb 10 '15 at 14:47

Another distinction is that "extrapolate" is typically used in the form "extrapolate from", with a reference to the previous data you are extrapolating from. This is one reason it "feels" more grounded in fact, though there is always a lot of gray area.

• Thank you for your answer.How about if we compare "to forecast", "to project " and " to extrapolate"..for example " the sale team projects/extrapolates that sales will rise next year" – Mrt Feb 10 '15 at 20:52
• I see myself responsible to welcome you to ELL.SE. And I don't think there's really anything wrong with this answer. However, it was better as a comment. I realize you couldn't have done such thing, as your rep doesn't allow you. – M.A.R. Feb 10 '15 at 20:55
• I'm not certain that "extrapolate from" is overwhelmingly more common than usages without "from". When I look for example sentences containing extrapolate it's a pretty mixed bag. – ColleenV Feb 10 '15 at 23:38