Vocabulary: some “-ibles”

When you tutor English, you still need to discuss spelling – believe it or not.

When I was a kid, I often wondered which words were “ible” and which were “able”.  In time, I realized that I used more “able” words than “ible” ones.  “Able”, I reasoned, made much more sense anyway:  If you are “able” to do something, you can do it.  “Ible”, by itself, has no meaning.

Every once and a while, though, an –ible word would show itself.  Possible, of course, was familiar; later, in grade 4, I met edible.  In quiet times I wondered if a system existed that would tell you when to use -ible vs -able.

Like so many of my school-age ponderings, my quest for an explanation of when to use –ible vs -able faded away.  It was gradually replaced by an acceptance that both endings had their places.  You could check the dictionary if you weren’t sure; otherwise, like so many other things about English, you just “had to know.”

I’ve put together a list of some -ible words for your amusement:

  1. convertible
  2. indelible:  permanent.  A laundry marker is indelible.
  3. defensible
  4. feasible
  5. collectible
  6. inexhaustible
  7. gullible:  easily fooled.
  8. credible
  9. corruptible
  10. reprehensible

Of course, with spell checkers, some people argue the –ible vs -able issue is academic.  Maybe they’re right….

The changes between 1980 and 1990 were incredible.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Essay Writing: Some practical considerations

Tutoring English, advice can be more important than “how-to”.  Here, then, are some practical pointers to help your next essay.

Talking to my sister yesterday, she told me she’s had a flood of essays to mark this semester.  When your essay is amongst many others, you might have extra opportunity for reward.

Like anyone else, English professors possibly get tired of marking so many essays – especially if one after another shows the same tired errors and repetitive sentence structure.

If you can make your essay enjoyable to read (while still functioning as a valid essay, of course), your professor might likely be a little kinder about any errors you make, and a little happier about what you’ve done right.

Here are some tips you might find helpful:

  1. Make sure you prove your thesis.  This will help you stay on topic and make your essay straightforward reading.
  2. Proofread your essay for errors.  This tip sounds obvious, but many people I’ve talked to say they never proofread their work.  Remember:  spell checkers don’t catch everything!
  3. Vary your sentence length and structure.  Use some inversions and the odd compound sentence – although complex ones are better.  Keep sentence length to two and a half lines or less – most should be less.  Short sentences – as little as five words – can be very effective now and then.
  4. Connecting with the last point, use a variety of punctuation.  Consider a semicolon, colon, or dash where appropriate.
  5. Vocabulary:  use some less common, but more descriptive words where appropriate.
  6. (Potentially) Controversial:  if your essay is finished, but underweight, don’t “pad” it.  I think ten percent under the assigned word count is probably acceptable in most cases – as long as the essay follows all the other instructions given.  If your word count is less than 90 percent of the assigned length, you’ll probably need another supporting paragraph in the body to make up the shortfall.

With reference to points 4 and 5:  you needn’t do those strategies more than once a paragraph or even every other paragraph.

Of course, asking your professor about any of these points might yield some great feedback.  Believe it or not, I’ll be commenting on how to ask your professor questions in an upcoming post.

Happy Holidays.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Significant Figures: Adding and Subtracting

We continue our commentary on significant figures – aka significant digits – with how to add and subtract them.  A chemistry or physics tutor deals with this topic periodically.

If you look over my last few posts, you’ll see the accumulation of articles on significant digits.  Today, we cover adding and subtracting, which is a bit trickier than multiplying and dividing.

With adding or subtracting, you need to see the numbers arranged in a column to understand what to do.

Take, for example, 54.28-49.329.

Step 1:  Write the calculation in a column.

Step 2:  Notice the last place on the right where both numbers have a digit.  Draw a cut-off line there.

Step 3:  Realize that any figures to the right of the cutoff are not significant.  This is why, in the case above, the answer is 4.95 in significant figures.

While 54.28 has four significant digits and 49.329 has five, the answer has only three.  Significant figures can be destroyed by subtraction, whereas they can’t be by multiplication or division.  (See the previous post to understand why.)

Here’s another example:  adding this time.

6.26 + 9.1

Here’s our result:

Note that, because the next digit is greater than 5, we round up, giving 15.4.

As we’ve seen, subtraction can destroy significant figures.  Can addition create them?  See for yourself:

Apparently, each addend has only two sigificant digits, while the answer has three.  Some professors may raise their eyebrows at this:)

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Significant Figures: Multiplying and Dividing

When you tutor physics or chemistry, most calculations require management of significant figures (aka significant digits).  Today, we’ll look at multiplying and dividing.

We know from earlier posts (see the previous one here) why significant figures are needed and how to tell when zeros are significant. Now, we’ll discuss how to report the result of a calculation to the correct number of significant figures.

Remember that, “on sight”, all nonzero digits are significant. The rules for zeros, once again, are covered here. However, once you do a calculation, you must apply other rules to determine how many significant digits are in the answer.

With mutliplying and dividing, the method is simple:

1)  Decide which input number has the least number of significant figures.

2)  The least number from 1) is the proper number of significant figures for your answer.

Putting it a different way:  the correct number of significant figures for the answer is how many the input with the least of them has.

Consider an example:

75.04 x 0.407

We know that 75.04 has four significant digits, while 0.407 has 3.  Our answer must then have three significant digits.

Of course, as often happens, the calculator gives us more than the proper number of significant digits:

75.04 x 0.407 = 30.54128

We round our answer to three significant digits:

30.54128 ≈ 30.5

Just to review:  We were multiplying.  One input number had four significant digits and one had three.  Therefore, we rounded our answer to three significant digits.

Here’s another example:

0.5695 ÷ 1.7 = 0.335

We know that 0.5674 has four significant digits while 1.7 has only two.  Our answer, therefore, should have two significant digits:

0.335 ≈ 0.34

(Since the next digit is 5 or more, we round up to 0.34.)

The method explained in this post applies to multiplying and dividing with significant digits.  Adding and subtracting use a different method, which will be covered in a future post.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Significant Figures: Zeros

Tutoring physics or chemistry, significant figures are part of the landscape.  Knowing when zero is significant can be tricky.

In this, our second installment on significant figures (see the first one here), we start on the practical question,  “What digits are significant?”  However, that question might be a bit ambitious for one post.  We’ll restrict today’s article to “When is zero significant?”

Numbers that result from calculations have other factors to consider.  For the purpose of this talk, we’ll assume we know nothing about how the number came about; we only know it “by sight”.

Case 1:  a zero between two nonzero digits.

Simple:  Always significant.

Example:  In the number 502, zero is significant.

Case 2:  a zero after a nonzero digit but before an unwritten decimal.

Simple:  Not significant.

Example:  In 7600 the zeros are not significant.

Case 3:  a zero after a nonzero digit, but before a written decimal.

Simple:  Always significant.

Example:  In 7600. the zeros are significant.

Yes, indeed:  120 and 120. are not the same, from a science point of view.  Their values are equal from the point of view of doing calculations, but the results of the calculations have different meaning.

Case 4:  Zeros to the left of the first nonzero digit.

Simple:  Never significant.

Example:  in 0.0035, the zeros are not significant.

Case 5:  Zeros following a nonzero digit and a decimal point:

Simple:  Always significant.

Example:  in 0.003 500 00, the four zeros following the five are significant.

Example:  in 13.0, the zero is significant.

We have another situation unique to significant figures:  12 and 12.0 are not the same.  80.1 and 80.100 are not the same, either, from the point of view of sig figs.

Let’s say you want a zero to be significant, but normal rules say it’s not.  Consider the following number:

23 000

We know that, since the decimal is unwritten, the three zeros are not significant.  However, what if, from the measurement itself, you know that the first zero actually is significant?

You can put a dash over the 0 that normally wouldn’t be significant to show that it is:

Now that people use scientific notation (which we’ll need to discuss in a future post), you rarely see the dashes anymore.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Significant Figures: Genesis

When you tutor chemistry or physics, significant figures are a constant theme.  Some people call them significant digits.  We’ll start our explanation today.

Bill:  How heavy is that boat?

Joe:  Maybe 30 tons, give or take a couple.

Bill:  Then it’s 30 tons, 40 pounds.  I see a sandbag on deck.

The conversation above illustrates the concept of significant figures.  If a boat’s mass is 30 tons, give or take two tons, that puts its mass anywhere from 28 to 32 tons.  In that context, a 40 pound sandbag is not significant:  we can’t know the mass to the exact number of pounds, when we don’t even know the exact number of tons.

Here’s another illustration:  let’s say you know Susan’s house is 3km from Sherry’s.  Sherry lives in a town that’s around 800km away.  However, “around 800km” means between 750km and 850km.  Can you say that if Sherry lives “around 800km” away, Susan must live 803km away?  Once again, the 3km difference is not significant, since there is  a 100km range in the actual distance to the town.

Physics and chemistry use significant figures (sig figs)- aka, significant digits (sig digs) -to reflect the reliability of any measurement – i.e., how precisely that measurement is actually known.  The system is relatively straightforward in most cases, but takes some getting used to.

Now that we know the purpose of significant figures, we’ll discuss how to treat them in the next few posts.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Recombinant DNA

Tutoring Biology 12, you sometimes talk about recombinant DNA.  We’ll briefly look at what it is and why it’s used.

Recombinant  DNA (rDNA) contains DNA from more than one organism.  The industrial uses I know of involve inserting specific genes from one species into the DNA of a host.

One application of rDNA is the production of human insulin.  In past times, insulin from cows or pigs was used for treating diabetes.  Not surprisingly, some people had reactions to it; though similar to human insulin, it wasn’t identical.  Now, human insulin can be given.  The human insulin is not produced by humans, though.  Instead, it’s produced by E. coli bacteria whose DNA is recombinant, containing the human gene for insulin production.  Since the E. coli bacteria contain the human insulin gene, they produce human insulin.

Genetic modification is, potentially, a controversial topic.  However, it certainly has some practical uses.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.


Biology 12, Module 2:  Cell Biology 2.  2007:  Open School BC.

Inquiry into Life, Eleventh Edition, Sylvia S. Mader.  2006:  McGraw-Hill.