¡La Esquina de la Gramática! Rule 13

The adverb “solo” and the demonstrative pronouns, no accent marks anymore

The word “solo”, when it is an adverb and means “solamente” (Solo llevaba un par de monedas en el bolsillo), as when it is an adjective (No me gusta estar solo), and the demonstratives “este”, “ese” and “aquel” in feminine and plurals modes as well, when they are pronouns (Este es tonto; Quiero aquella) or determiners (aquellos tipos, la chica esa) should not have an accent mark according to the general accent rules.

Previous grammar rules advised on the use of accent marks in the adverb “solo” and the demonstrative pronouns so there was no confusion with the adjective “solo” and the demonstrative determiners, when both interpretations were possible in one sentence. Below is an example:

Trabaja solo los domingos: it could be interpreted as someone who only works on Sundays, or works by himself on Sundays.

Also, the context of a sentence often resolves doubts about double meaning (ambiguity).

Source: http://www.rae.es