The friendship which we conceive for a man is different from that with which a woman affects us, even where there is no mixture of any grosser passion.
 Adam Smith, The Theory of Moral Sentiments (1759). copy citation

Context

“The sentiment of friendship, for example, which we feel for an old man is different from that which we feel for a young: that which we entertain for an austere man different from that which we feel for one of softer and gentler manners: and that again from what we feel for one of gay vivacity and spirit. The friendship which we conceive for a man is different from that with which a woman affects us, even where there is no mixture of any grosser passion. What author could enumerate and ascertain these and all the other infinite varieties which this sentiment is capable of undergoing? But still the general sentiment of friendship and familiar attachment which is common to them all, may be ascertained with a sufficient degree of accuracy.” source