Missing parts

Sometimes when people give you arguments, they will leave out parts of the argument. This may be because those parts are things that we all know, or maybe they think they don’t need to state every single reason explicitly, or maybe they have rhetorical reasons for leaving parts out.

If in some part of my argument, I need something simple like

• The Moon is not a planet.

I don’t really need to say this, because I know that you know this. And it would be pedantic or perhaps insulting to tell you. And sometimes, it’s more effective to leave it out.

Here’s an example of an argument with missing parts, taken from the cabaret song Maybe This Time:

Everybody loves a winner, so nobody loves me.

• I’m not a winner.

(begin{array}{ll} text{P1} & text{Everybody loves a winner.} text{P2} & text{[I’m not a winner.]} &text{Therefore,} text{C} & text{Nobody loves me.} end{array})

Recently, whilst I was on sabbatical in Scotland, I thought I saw the Loch Ness Monster. Turns out that all the sightings of the Loch Ness Monster are actually people mistaking logs for non-logs.

• I did not see the Loch Ness Monster.

(begin{array}{ll} text{P1} & text{Whilst I was on sabbatical in Scotland, I thought I saw the } & text{Loch Ness Monster.} text{P2} & text{All the sightings of the Loch Ness Monster are actually } & text{people mistaking logs for non-logs.} &text{Therefore,} text{C} & text{[I did not see the Loch Ness Monster.]} end{array})

As above, we put the conclusion in brackets to indicate that it was suppressed.

You need to be careful when formulating the suppressed conclusion. You want to find a conclusion that matches the reasons. You don’t want to put in a conclusion that wouldn’t be supported by the premises. This is not always easy, and we’ll have a chance to come to examples with suppressed premises and conclusions.