Je bohuzel mnohem komplikovanesji. "Relation" i "relationship" mohou byt jak mezi lidmi tak mezi vecmi. Mohou byt i mezi clovekem a veci. A synomymy nejsou. Rozdil se lisi podle kontextu, ale mozna par dialogu vam to trochu ujasni.
"What's the relation between Peter and Paul?"
"Peter is Paul's stepfather".
"What's their relationship like?"
"Not very close. They tend to avoid each other."
"Is there any relation between household income and life expectancy?"
"Yes, people in richer households tend to live longer."
"How strong is that relationship?"
"Moderately strong, and highly statistically significant. Income explains 20% of the variance in life expectancy, and is significant at the level p < 0.0001"