kind of, kinds of, kinda, sort of, sorts of

It is preferable to write this kind of and that kind of (or these kinds of and those kinds of).

• This kind of honey has a strong scent of flowers.
• Those kinds of plastic containers cannot be used in the microwave.

Refrain from mixing singular and plural, as in these kind of or those kind of. (However, the phrase kind of in the singular may be followed by a plural noun.)

• Incorrect: If you don’t like those kind of socks, don’t wear them.
• Correct: If you don’t like that kind of socks, don’t wear them.

• Incorrect: These kind of dogs are better suited to families.
• Correct: These kinds of dogs are better suited to families.

The same rule applies to sort of and sorts of.

• That sort of behaviour will not be tolerated.
• What sort of biscuits do you like, Paul?
• These sorts of things usually work themselves out.

In formal writing, avoid the non-standard kinda, meaning “rather” or “somewhat.”

• Informal: He looks kinda elegant in his uniform.
• Formal: He looks elegant (or rather elegant) in his uniform.