Binomials are pairs of words in a set order, joined by a small linking word, usually and, sometimes or. The order is fixed for each pair, so learn it with the phrase. This card takes the and pairs: pros and cons means the advantages and disadvantages, ups and downs means the good and bad times, and ins and outs means all the small details of how something works. Learn each one as a single chunk.
Fixed pairs joined by 'and'
pros and cons /proʊz ənd kɑnz/ — Before we decide, let's weigh the pros and cons of moving the office.
ups and downs /ʌps ənd daʊnz/ — Every long friendship has its ups and downs.
ins and outs /ɪnz ənd aʊts/ — After a month on the job, she knew the ins and outs of the whole system.
Not ""We need to weigh the cons and pros carefully." (order flipped)" — say ""We need to weigh the pros and cons carefully." (fixed order)". The pair is always pros and cons, never 'cons and pros'. Binomials are fixed units; you can't reverse the words.
Try it: Which sentence uses the binomial in its correct fixed form? (I know the ins and outs of how this office runs. / I know the outs and ins of how this office runs. / I know the ins or outs of how this office runs.) Answer: I know the ins and outs of how this office runs. — The fixed pair is 'ins and outs', meaning all the small workings of something, so both the order and the connector are set. 'outs and ins' reverses the locked order, and 'ins or outs' swaps in the wrong connector; this binomial always takes 'and'.
Pairs about time and quantity
Some binomials describe time or amount. sooner or later means eventually, at some point; more or less means approximately or roughly; and trial and error means learning by trying, failing, and adjusting. Notice that some use and and some use or, and you can't swap them.
sooner or later /ˈsunər ɔr ˈleɪtər/ — You can put it off, but sooner or later you'll have to reply to that email.
more or less /mɔr ɔr lɛs/ — The repairs are more or less finished; just a few small things left.
trial and error /ˈtraɪəl ənd ˈɛrər/ — I learned to cook mostly through trial and error, not from recipes.
Try it: Choose the correct binomial: "You can avoid it for now, but ___ you'll have to face the deadline." (sooner or later / sooner or never / sooner and later) Answer: sooner or later — 'Sooner or later' means eventually, which fits a deadline you can't escape forever. 'Sooner or never' isn't a real binomial (the fixed second word is 'later'), and 'sooner and later' swaps the connector; this pair takes 'or', not 'and'.
Try it: Which sentence uses 'more or less' correctly to mean 'approximately'? (The room holds more or less fifty people. / The room holds less or more fifty people. / The room holds more and less fifty people.) Answer: The room holds more or less fifty people. — 'More or less' means roughly, so 'more or less fifty' reads as 'about fifty'. 'Less or more' reverses the locked order, and 'more and less' uses the wrong connector; this binomial is joined by 'or', not 'and'.