The Truth, The Whole Truth, And Nothing But the Truth

"It can't be 'partly' true, it's either true or it's not!" he insisted.

"Well," I wryly replied, "that's partly true."

So what does "true" mean anyway? Can something be partially true and partially false? Or is a statement all true or false if it contains any part which is false? It's not so clear. For, in truth, the question of what is "true" is one of hotly contested debate for centuries that filled many volumes and is well beyond the scope of this site or post. Here's the Wikipedia entry on Truth.

What my friend meant was true in the Boolean sense. "A and B" is true if and only if "A" is true and "B" is true. So, in that sense, his statement was true.

I contend, in contrast, that outside the nice little world of pure logic, things get a lot stickier and it starts to make more sense to think about propositions as wholly or partly true. In fact, in real world examples, it starts to become harder to find propositions which are wholly and unambiguously true.

The stock market crash of 1929 caused the Great Depression is true, says I, but it's not an uncontested statement, if generally accepted. And it's not the whole story. Some would argue it's not even the primary cause. They'd argue that absent other factors, say, the reaction of the Federal Reserve, the recession might not have turned into a depression.

This leads to another observation, "partly" or "partially" true might mean that the statement is true in part and false in part or it might mean that it is only part of what is true. In everyday use, people use "partly true" to avoid rejecting whole cloth a statement which contains some truth but not entirely or to hedge particularly when they cannot dispute a statement as stated but feel that there are attenuating or mitigating factors that are of equal or greater importance that have not yet presented.