## Forbidden words and phrases for Physics problem solutions

These phrases do not add anything to a solution, and should be avoided.

"Assume". Do not assume! Either prove it, or don't use it.
What should be assumed will be given in the problem statement.

"We know that..." How
do you know?

"By symmetry..." Always discuss exactly which symmetries exist,
and how they affect your analysis!

"Clearly.." If it is really clear, this word is superfluous. If it is not clear, this statement can get you into real trouble.

"It is obvious that..." Same as above.

"This is easily done." See above.

"it" Usually ambiguous: use the appropriate noun.

"this" "that" Same as above

"From Tables.." Not in Physics 785/485! In classes where tables
are allowed, always give the precise reference (title of table, formula number,
page number etc.)

"just" almost always leads to problems.

"My result shows me that..." How does it show you?

"This can be used to show that..." variant of above

"We can say that.." Just say it!

"We can write.." Just write it!

"Note that.." Often used instead of a properly reasoned argument.

"From Mathematica." If you use software like this always show the input
to the program and its output. Be aware that Mathematica makes errors!
Always CHECK the results.

Frequently mis-used symbols and phrases:

-----> When used correctly, this symbol
means "tends to" or "becomes".

Double arrow ("implies" symbol). If you cannot substitute the word
"implies", you are misusing the symbol. It should never appear
pointing downward, upward, or any direction other than to the right.

The "infinity" symbol may ONLY appear after the arrow ------>. It
must never appear after an equals sign, after a mathematical operator such
as +, - or ×, or in the numerator or denominator of a fraction.

The symbol 0 (zero) may never appear in the denominator of a fraction.
If you are trying to do this, you probably need to take a limit.

"By definition.." or " ... is defined as...". Always CHECK
the definition before you make this assertion. 9 times out of 10 when
students say this it is not true.

An equals sign needs something on both sides of it, not just one.

Mathematical operators may not be placed in sequence: for example "2 + -
3" is not legal. You may need to use parentheses: "2 +(-3)" is
fine.

"So", "Thus" and "Therefore" should *conclude* an argument, not *substitute
for* an argument.