Since Twitter is currently struggling with the conundrum of how to assign gender to inanimate objects, I thought I’d contribute some interesting ideas from languages with a masculine-feminine gender system. There are basically three common approaches:

• Semantic (classification based on what a noun means and the properties of its referents)
• Phonological (classification based on the sound of the noun)
• Morphological (classification based on the inflections or derivational suffixes a noun contains or takes)

If we focus on the semantic, it is not uncommon for a language with a masc-fem system to have a systematic semantic framework for assigning inanimate objects to genders. Here’s an example from Manambu, from Aikhenvald’s grammar of the language:

• Humans
  • Males → Masculine
  • Females → Feminine
• Many animals
  • Large size → Masculine
  • Small size → Feminine
• Inanimates and lower animates
  • Long and large → Masculine
  • Round and small → Female
• Mass nouns
  • Large quantity → Masculine
  • Small quantity → Feminine
• Natural phenomena
  • Complete/intense → Masculine
  • Otherwise → Feminine

The basic principle at work here should be obvious, which is that, if gender is not inherently relevant to an object, then large and long and/or powerful things are assigned masculine, and small and round things are assigned feminine.

According to The Papuan Languages of New Guinea, in Mianmin similar associations of narrowness with masculine and roundness with the feminine occur, but with inverted quantity associations with plural and mass nouns: large quantities are feminine while small quantities are masculine.

Similar associations, especially of size and extendedness, occur in other languages. In Alamblak, a language distantly related to Manambu, short, squat or wide objects are feminine, and tall, long, slender or narrow objects are masculine according to Classifiers: A Typology of Noun Classification Devices.

The same book claims that similar associations even occur in some European languages. The following gender associations are claimed to occur in the Cantabrian dialect of Spanish, which are not present in the standard language:

Masculine	Feminine
Male	Female
Small	Large
Narrow	Wide
Vertical	Horizontal
Tall	Squat
Phallic	Supine
Coarse	Smooth
Dark	Light
Deprecatory	Approbatory
Derived	Primary
Occasional	Familiar

Many of these features have an obvious biological or cultural basis. But, in summary, by far the most common cross-linguistic association seems to be extendedness (long, thin, …) with masculine, and rounded with feminine. Other features like size seem more variable depending on the language in question.

I hope this helps!